# sqlglot.helper API documentation

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# sqlglot.helper

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      1from __future__ import annotations
      2
      3import datetime
      4import inspect
      5import logging
      6import re
      7import sys
      8import typing as t
      9from collections.abc import Collection, Set
     10from contextlib import contextmanager
     11from copy import copy
     12from difflib import get_close_matches
     13from enum import Enum
     14from itertools import count
     15
     16if t.TYPE_CHECKING:
     17    from sqlglot import exp
     18    from sqlglot._typing import A, E, T
     19    from sqlglot.dialects.dialect import DialectType
     20    from sqlglot.expressions import Expression
     21
     22
     23CAMEL_CASE_PATTERN = re.compile("(?<!^)(?=[A-Z])")
     24PYTHON_VERSION = sys.version_info[:2]
     25logger = logging.getLogger("sqlglot")
     26
     27
     28class AutoName(Enum):
     29    """
     30    This is used for creating Enum classes where `auto()` is the string form
     31    of the corresponding enum's identifier (e.g. FOO.value results in "FOO").
     32
     33    Reference: https://docs.python.org/3/howto/enum.html#using-automatic-values
     34    """
     35
     36    def _generate_next_value_(name, _start, _count, _last_values):
     37        return name
     38
     39
     40class classproperty(property):
     41    """
     42    Similar to a normal property but works for class methods
     43    """
     44
     45    def __get__(self, obj: t.Any, owner: t.Any = None) -> t.Any:
     46        return classmethod(self.fget).__get__(None, owner)()  # type: ignore
     47
     48
     49def suggest_closest_match_and_fail(
     50    kind: str,
     51    word: str,
     52    possibilities: t.Iterable[str],
     53) -> None:
     54    close_matches = get_close_matches(word, possibilities, n=1)
     55
     56    similar = seq_get(close_matches, 0) or ""
     57    if similar:
     58        similar = f" Did you mean {similar}?"
     59
     60    raise ValueError(f"Unknown {kind} '{word}'.{similar}")
     61
     62
     63def seq_get(seq: t.Sequence[T], index: int) -> t.Optional[T]:
     64    """Returns the value in `seq` at position `index`, or `None` if `index` is out of bounds."""
     65    try:
     66        return seq[index]
     67    except IndexError:
     68        return None
     69
     70
     71@t.overload
     72def ensure_list(value: t.Collection[T]) -> t.List[T]: ...
     73
     74
     75@t.overload
     76def ensure_list(value: None) -> t.List: ...
     77
     78
     79@t.overload
     80def ensure_list(value: T) -> t.List[T]: ...
     81
     82
     83def ensure_list(value):
     84    """
     85    Ensures that a value is a list, otherwise casts or wraps it into one.
     86
     87    Args:
     88        value: The value of interest.
     89
     90    Returns:
     91        The value cast as a list if it's a list or a tuple, or else the value wrapped in a list.
     92    """
     93    if value is None:
     94        return []
     95    if isinstance(value, (list, tuple)):
     96        return list(value)
     97
     98    return [value]
     99
    100
    101@t.overload
    102def ensure_collection(value: t.Collection[T]) -> t.Collection[T]: ...
    103
    104
    105@t.overload
    106def ensure_collection(value: T) -> t.Collection[T]: ...
    107
    108
    109def ensure_collection(value):
    110    """
    111    Ensures that a value is a collection (excluding `str` and `bytes`), otherwise wraps it into a list.
    112
    113    Args:
    114        value: The value of interest.
    115
    116    Returns:
    117        The value if it's a collection, or else the value wrapped in a list.
    118    """
    119    if value is None:
    120        return []
    121    return (
    122        value if isinstance(value, Collection) and not isinstance(value, (str, bytes)) else [value]
    123    )
    124
    125
    126def csv(*args: str, sep: str = ", ") -> str:
    127    """
    128    Formats any number of string arguments as CSV.
    129
    130    Args:
    131        args: The string arguments to format.
    132        sep: The argument separator.
    133
    134    Returns:
    135        The arguments formatted as a CSV string.
    136    """
    137    return sep.join(arg for arg in args if arg)
    138
    139
    140def subclasses(
    141    module_name: str,
    142    classes: t.Type | t.Tuple[t.Type, ...],
    143    exclude: t.Type | t.Tuple[t.Type, ...] = (),
    144) -> t.List[t.Type]:
    145    """
    146    Returns all subclasses for a collection of classes, possibly excluding some of them.
    147
    148    Args:
    149        module_name: The name of the module to search for subclasses in.
    150        classes: Class(es) we want to find the subclasses of.
    151        exclude: Class(es) we want to exclude from the returned list.
    152
    153    Returns:
    154        The target subclasses.
    155    """
    156    return [
    157        obj
    158        for _, obj in inspect.getmembers(
    159            sys.modules[module_name],
    160            lambda obj: inspect.isclass(obj) and issubclass(obj, classes) and obj not in exclude,
    161        )
    162    ]
    163
    164
    165def apply_index_offset(
    166    this: exp.Expression,
    167    expressions: t.List[E],
    168    offset: int,
    169    dialect: DialectType = None,
    170) -> t.List[E]:
    171    """
    172    Applies an offset to a given integer literal expression.
    173
    174    Args:
    175        this: The target of the index.
    176        expressions: The expression the offset will be applied to, wrapped in a list.
    177        offset: The offset that will be applied.
    178        dialect: the dialect of interest.
    179
    180    Returns:
    181        The original expression with the offset applied to it, wrapped in a list. If the provided
    182        `expressions` argument contains more than one expression, it's returned unaffected.
    183    """
    184    if not offset or len(expressions) != 1:
    185        return expressions
    186
    187    expression = expressions[0]
    188
    189    from sqlglot import exp
    190    from sqlglot.optimizer.annotate_types import annotate_types
    191    from sqlglot.optimizer.simplify import simplify
    192
    193    if not this.type:
    194        annotate_types(this, dialect=dialect)
    195
    196    if t.cast(exp.DataType, this.type).this not in (
    197        exp.DataType.Type.UNKNOWN,
    198        exp.DataType.Type.ARRAY,
    199    ):
    200        return expressions
    201
    202    if not expression.type:
    203        annotate_types(expression, dialect=dialect)
    204
    205    if t.cast(exp.DataType, expression.type).this in exp.DataType.INTEGER_TYPES:
    206        logger.info("Applying array index offset (%s)", offset)
    207        expression = simplify(expression + offset)
    208        return [expression]
    209
    210    return expressions
    211
    212
    213def camel_to_snake_case(name: str) -> str:
    214    """Converts `name` from camelCase to snake_case and returns the result."""
    215    return CAMEL_CASE_PATTERN.sub("_", name).upper()
    216
    217
    218def while_changing(expression: Expression, func: t.Callable[[Expression], E]) -> E:
    219    """
    220    Applies a transformation to a given expression until a fix point is reached.
    221
    222    Args:
    223        expression: The expression to be transformed.
    224        func: The transformation to be applied.
    225
    226    Returns:
    227        The transformed expression.
    228    """
    229    end_hash: t.Optional[int] = None
    230
    231    while True:
    232        # No need to walk the AST– we've already cached the hashes in the previous iteration
    233        if end_hash is None:
    234            for n in reversed(tuple(expression.walk())):
    235                n._hash = hash(n)
    236
    237        start_hash = hash(expression)
    238        expression = func(expression)
    239
    240        expression_nodes = tuple(expression.walk())
    241
    242        # Uncache previous caches so we can recompute them
    243        for n in reversed(expression_nodes):
    244            n._hash = None
    245            n._hash = hash(n)
    246
    247        end_hash = hash(expression)
    248
    249        if start_hash == end_hash:
    250            # ... and reset the hash so we don't risk it becoming out of date if a mutation happens
    251            for n in expression_nodes:
    252                n._hash = None
    253
    254            break
    255
    256    return expression
    257
    258
    259def tsort(dag: t.Dict[T, t.Set[T]]) -> t.List[T]:
    260    """
    261    Sorts a given directed acyclic graph in topological order.
    262
    263    Args:
    264        dag: The graph to be sorted.
    265
    266    Returns:
    267        A list that contains all of the graph's nodes in topological order.
    268    """
    269    result = []
    270
    271    for node, deps in tuple(dag.items()):
    272        for dep in deps:
    273            if dep not in dag:
    274                dag[dep] = set()
    275
    276    while dag:
    277        current = {node for node, deps in dag.items() if not deps}
    278
    279        if not current:
    280            raise ValueError("Cycle error")
    281
    282        for node in current:
    283            dag.pop(node)
    284
    285        for deps in dag.values():
    286            deps -= current
    287
    288        result.extend(sorted(current))  # type: ignore
    289
    290    return result
    291
    292
    293def open_file(file_name: str) -> t.TextIO:
    294    """Open a file that may be compressed as gzip and return it in universal newline mode."""
    295    with open(file_name, "rb") as f:
    296        gzipped = f.read(2) == b"\x1f\x8b"
    297
    298    if gzipped:
    299        import gzip
    300
    301        return gzip.open(file_name, "rt", newline="")
    302
    303    return open(file_name, encoding="utf-8", newline="")
    304
    305
    306@contextmanager
    307def csv_reader(read_csv: exp.ReadCSV) -> t.Any:
    308    """
    309    Returns a csv reader given the expression `READ_CSV(name, ['delimiter', '|', ...])`.
    310
    311    Args:
    312        read_csv: A `ReadCSV` function call.
    313
    314    Yields:
    315        A python csv reader.
    316    """
    317    args = read_csv.expressions
    318    file = open_file(read_csv.name)
    319
    320    delimiter = ","
    321    args = iter(arg.name for arg in args)  # type: ignore
    322    for k, v in zip(args, args):
    323        if k == "delimiter":
    324            delimiter = v
    325
    326    try:
    327        import csv as csv_
    328
    329        yield csv_.reader(file, delimiter=delimiter)
    330    finally:
    331        file.close()
    332
    333
    334def find_new_name(taken: t.Collection[str], base: str) -> str:
    335    """
    336    Searches for a new name.
    337
    338    Args:
    339        taken: A collection of taken names.
    340        base: Base name to alter.
    341
    342    Returns:
    343        The new, available name.
    344    """
    345    if base not in taken:
    346        return base
    347
    348    i = 2
    349    new = f"{base}_{i}"
    350    while new in taken:
    351        i += 1
    352        new = f"{base}_{i}"
    353
    354    return new
    355
    356
    357def is_int(text: str) -> bool:
    358    return is_type(text, int)
    359
    360
    361def is_float(text: str) -> bool:
    362    return is_type(text, float)
    363
    364
    365def is_type(text: str, target_type: t.Type) -> bool:
    366    try:
    367        target_type(text)
    368        return True
    369    except ValueError:
    370        return False
    371
    372
    373def name_sequence(prefix: str) -> t.Callable[[], str]:
    374    """Returns a name generator given a prefix (e.g. a0, a1, a2, ... if the prefix is "a")."""
    375    sequence = count()
    376    return lambda: f"{prefix}{next(sequence)}"
    377
    378
    379def object_to_dict(obj: t.Any, **kwargs) -> t.Dict:
    380    """Returns a dictionary created from an object's attributes."""
    381    return {
    382        **{k: v.copy() if hasattr(v, "copy") else copy(v) for k, v in vars(obj).items()},
    383        **kwargs,
    384    }
    385
    386
    387def split_num_words(
    388    value: str, sep: str, min_num_words: int, fill_from_start: bool = True
    389) -> t.List[t.Optional[str]]:
    390    """
    391    Perform a split on a value and return N words as a result with `None` used for words that don't exist.
    392
    393    Args:
    394        value: The value to be split.
    395        sep: The value to use to split on.
    396        min_num_words: The minimum number of words that are going to be in the result.
    397        fill_from_start: Indicates that if `None` values should be inserted at the start or end of the list.
    398
    399    Examples:
    400        >>> split_num_words("db.table", ".", 3)
    401        [None, 'db', 'table']
    402        >>> split_num_words("db.table", ".", 3, fill_from_start=False)
    403        ['db', 'table', None]
    404        >>> split_num_words("db.table", ".", 1)
    405        ['db', 'table']
    406
    407    Returns:
    408        The list of words returned by `split`, possibly augmented by a number of `None` values.
    409    """
    410    words = value.split(sep)
    411    if fill_from_start:
    412        return [None] * (min_num_words - len(words)) + words
    413    return words + [None] * (min_num_words - len(words))
    414
    415
    416def is_iterable(value: t.Any) -> bool:
    417    """
    418    Checks if the value is an iterable, excluding the types `str` and `bytes`.
    419
    420    Examples:
    421        >>> is_iterable([1,2])
    422        True
    423        >>> is_iterable("test")
    424        False
    425
    426    Args:
    427        value: The value to check if it is an iterable.
    428
    429    Returns:
    430        A `bool` value indicating if it is an iterable.
    431    """
    432    from sqlglot import Expression
    433
    434    return hasattr(value, "__iter__") and not isinstance(value, (str, bytes, Expression))
    435
    436
    437def flatten(values: t.Iterable[t.Iterable[t.Any] | t.Any]) -> t.Iterator[t.Any]:
    438    """
    439    Flattens an iterable that can contain both iterable and non-iterable elements. Objects of
    440    type `str` and `bytes` are not regarded as iterables.
    441
    442    Examples:
    443        >>> list(flatten([[1, 2], 3, {4}, (5, "bla")]))
    444        [1, 2, 3, 4, 5, 'bla']
    445        >>> list(flatten([1, 2, 3]))
    446        [1, 2, 3]
    447
    448    Args:
    449        values: The value to be flattened.
    450
    451    Yields:
    452        Non-iterable elements in `values`.
    453    """
    454    for value in values:
    455        if is_iterable(value):
    456            yield from flatten(value)
    457        else:
    458            yield value
    459
    460
    461def dict_depth(d: t.Dict) -> int:
    462    """
    463    Get the nesting depth of a dictionary.
    464
    465    Example:
    466        >>> dict_depth(None)
    467        0
    468        >>> dict_depth({})
    469        1
    470        >>> dict_depth({"a": "b"})
    471        1
    472        >>> dict_depth({"a": {}})
    473        2
    474        >>> dict_depth({"a": {"b": {}}})
    475        3
    476    """
    477    try:
    478        return 1 + dict_depth(next(iter(d.values())))
    479    except AttributeError:
    480        # d doesn't have attribute "values"
    481        return 0
    482    except StopIteration:
    483        # d.values() returns an empty sequence
    484        return 1
    485
    486
    487def first(it: t.Iterable[T]) -> T:
    488    """Returns the first element from an iterable (useful for sets)."""
    489    return next(i for i in it)
    490
    491
    492def to_bool(value: t.Optional[str | bool]) -> t.Optional[str | bool]:
    493    if isinstance(value, bool) or value is None:
    494        return value
    495
    496    # Coerce the value to boolean if it matches to the truthy/falsy values below
    497    value_lower = value.lower()
    498    if value_lower in ("true", "1"):
    499        return True
    500    if value_lower in ("false", "0"):
    501        return False
    502
    503    return value
    504
    505
    506def merge_ranges(ranges: t.List[t.Tuple[A, A]]) -> t.List[t.Tuple[A, A]]:
    507    """
    508    Merges a sequence of ranges, represented as tuples (low, high) whose values
    509    belong to some totally-ordered set.
    510
    511    Example:
    512        >>> merge_ranges([(1, 3), (2, 6)])
    513        [(1, 6)]
    514    """
    515    if not ranges:
    516        return []
    517
    518    ranges = sorted(ranges)
    519
    520    merged = [ranges[0]]
    521
    522    for start, end in ranges[1:]:
    523        last_start, last_end = merged[-1]
    524
    525        if start <= last_end:
    526            merged[-1] = (last_start, max(last_end, end))
    527        else:
    528            merged.append((start, end))
    529
    530    return merged
    531
    532
    533def is_iso_date(text: str) -> bool:
    534    try:
    535        datetime.date.fromisoformat(text)
    536        return True
    537    except ValueError:
    538        return False
    539
    540
    541def is_iso_datetime(text: str) -> bool:
    542    try:
    543        datetime.datetime.fromisoformat(text)
    544        return True
    545    except ValueError:
    546        return False
    547
    548
    549# Interval units that operate on date components
    550DATE_UNITS = {"day", "week", "month", "quarter", "year", "year_month"}
    551
    552
    553def is_date_unit(expression: t.Optional[exp.Expression]) -> bool:
    554    return expression is not None and expression.name.lower() in DATE_UNITS
    555
    556
    557K = t.TypeVar("K")
    558V = t.TypeVar("V")
    559
    560
    561class SingleValuedMapping(t.Mapping[K, V]):
    562    """
    563    Mapping where all keys return the same value.
    564
    565    This rigamarole is meant to avoid copying keys, which was originally intended
    566    as an optimization while qualifying columns for tables with lots of columns.
    567    """
    568
    569    def __init__(self, keys: t.Collection[K], value: V):
    570        self._keys = keys if isinstance(keys, Set) else set(keys)
    571        self._value = value
    572
    573    def __getitem__(self, key: K) -> V:
    574        if key in self._keys:
    575            return self._value
    576        raise KeyError(key)
    577
    578    def __len__(self) -> int:
    579        return len(self._keys)
    580
    581    def __iter__(self) -> t.Iterator[K]:
    582        return iter(self._keys)

CAMEL_CASE_PATTERN = re.compile('(?<!^)(?=[A-Z])')
PYTHON_VERSION = (3, 10)
logger = <Logger sqlglot (WARNING)>
class AutoName(enum.Enum): View Source

    29class AutoName(Enum):
    30    """
    31    This is used for creating Enum classes where `auto()` is the string form
    32    of the corresponding enum's identifier (e.g. FOO.value results in "FOO").
    33
    34    Reference: https://docs.python.org/3/howto/enum.html#using-automatic-values
    35    """
    36
    37    def _generate_next_value_(name, _start, _count, _last_values):
    38        return name

This is used for creating Enum classes where `auto()` is the string form of the corresponding enum's identifier (e.g. FOO.value results in "FOO").

Reference: https://docs.python.org/3/howto/enum.html#using-automatic-values

class classproperty(builtins.property): View Source

    41class classproperty(property):
    42    """
    43    Similar to a normal property but works for class methods
    44    """
    45
    46    def __get__(self, obj: t.Any, owner: t.Any = None) -> t.Any:
    47        return classmethod(self.fget).__get__(None, owner)()  # type: ignore

Similar to a normal property but works for class methods

def suggest_closest_match_and_fail(kind: str, word: str, possibilities: Iterable[str]) -> None: View Source

    50def suggest_closest_match_and_fail(
    51    kind: str,
    52    word: str,
    53    possibilities: t.Iterable[str],
    54) -> None:
    55    close_matches = get_close_matches(word, possibilities, n=1)
    56
    57    similar = seq_get(close_matches, 0) or ""
    58    if similar:
    59        similar = f" Did you mean {similar}?"
    60
    61    raise ValueError(f"Unknown {kind} '{word}'.{similar}")

def seq_get(seq: Sequence[~T], index: int) -> Optional[~T]: View Source

    64def seq_get(seq: t.Sequence[T], index: int) -> t.Optional[T]:
    65    """Returns the value in `seq` at position `index`, or `None` if `index` is out of bounds."""
    66    try:
    67        return seq[index]
    68    except IndexError:
    69        return None

Returns the value in `seq` at position `index`, or `None` if `index` is out of bounds.

def ensure_list(value): View Source

    84def ensure_list(value):
    85    """
    86    Ensures that a value is a list, otherwise casts or wraps it into one.
    87
    88    Args:
    89        value: The value of interest.
    90
    91    Returns:
    92        The value cast as a list if it's a list or a tuple, or else the value wrapped in a list.
    93    """
    94    if value is None:
    95        return []
    96    if isinstance(value, (list, tuple)):
    97        return list(value)
    98
    99    return [value]

Ensures that a value is a list, otherwise casts or wraps it into one.

###### Arguments:

- value: The value of interest.

###### Returns:

> The value cast as a list if it's a list or a tuple, or else the value wrapped in a list.

def ensure_collection(value): View Source

    110def ensure_collection(value):
    111    """
    112    Ensures that a value is a collection (excluding `str` and `bytes`), otherwise wraps it into a list.
    113
    114    Args:
    115        value: The value of interest.
    116
    117    Returns:
    118        The value if it's a collection, or else the value wrapped in a list.
    119    """
    120    if value is None:
    121        return []
    122    return (
    123        value if isinstance(value, Collection) and not isinstance(value, (str, bytes)) else [value]
    124    )

Ensures that a value is a collection (excluding `str` and `bytes`), otherwise wraps it into a list.

###### Arguments:

- value: The value of interest.

###### Returns:

> The value if it's a collection, or else the value wrapped in a list.

def csv(*args: str, sep: str = ', ') -> str: View Source

    127def csv(*args: str, sep: str = ", ") -> str:
    128    """
    129    Formats any number of string arguments as CSV.
    130
    131    Args:
    132        args: The string arguments to format.
    133        sep: The argument separator.
    134
    135    Returns:
    136        The arguments formatted as a CSV string.
    137    """
    138    return sep.join(arg for arg in args if arg)

Formats any number of string arguments as CSV.

###### Arguments:

- args: The string arguments to format.
- sep: The argument separator.

###### Returns:

> The arguments formatted as a CSV string.

def subclasses( module_name: str, classes: Union[Type, Tuple[Type, ...]], exclude: Union[Type, Tuple[Type, ...]] = ()) -> List[Type]: View Source

    141def subclasses(
    142    module_name: str,
    143    classes: t.Type | t.Tuple[t.Type, ...],
    144    exclude: t.Type | t.Tuple[t.Type, ...] = (),
    145) -> t.List[t.Type]:
    146    """
    147    Returns all subclasses for a collection of classes, possibly excluding some of them.
    148
    149    Args:
    150        module_name: The name of the module to search for subclasses in.
    151        classes: Class(es) we want to find the subclasses of.
    152        exclude: Class(es) we want to exclude from the returned list.
    153
    154    Returns:
    155        The target subclasses.
    156    """
    157    return [
    158        obj
    159        for _, obj in inspect.getmembers(
    160            sys.modules[module_name],
    161            lambda obj: inspect.isclass(obj) and issubclass(obj, classes) and obj not in exclude,
    162        )
    163    ]

Returns all subclasses for a collection of classes, possibly excluding some of them.

###### Arguments:

- module_name: The name of the module to search for subclasses in.
- classes: Class(es) we want to find the subclasses of.
- exclude: Class(es) we want to exclude from the returned list.

###### Returns:

> The target subclasses.

def apply_index_offset( this: sqlglot.expressions.Expression, expressions: List[~E], offset: int, dialect: Union[str, sqlglot.dialects.Dialect , Type[ sqlglot.dialects.Dialect ], NoneType] = None) -> List[~E]: View Source

    166def apply_index_offset(
    167    this: exp.Expression,
    168    expressions: t.List[E],
    169    offset: int,
    170    dialect: DialectType = None,
    171) -> t.List[E]:
    172    """
    173    Applies an offset to a given integer literal expression.
    174
    175    Args:
    176        this: The target of the index.
    177        expressions: The expression the offset will be applied to, wrapped in a list.
    178        offset: The offset that will be applied.
    179        dialect: the dialect of interest.
    180
    181    Returns:
    182        The original expression with the offset applied to it, wrapped in a list. If the provided
    183        `expressions` argument contains more than one expression, it's returned unaffected.
    184    """
    185    if not offset or len(expressions) != 1:
    186        return expressions
    187
    188    expression = expressions[0]
    189
    190    from sqlglot import exp
    191    from sqlglot.optimizer.annotate_types import annotate_types
    192    from sqlglot.optimizer.simplify import simplify
    193
    194    if not this.type:
    195        annotate_types(this, dialect=dialect)
    196
    197    if t.cast(exp.DataType, this.type).this not in (
    198        exp.DataType.Type.UNKNOWN,
    199        exp.DataType.Type.ARRAY,
    200    ):
    201        return expressions
    202
    203    if not expression.type:
    204        annotate_types(expression, dialect=dialect)
    205
    206    if t.cast(exp.DataType, expression.type).this in exp.DataType.INTEGER_TYPES:
    207        logger.info("Applying array index offset (%s)", offset)
    208        expression = simplify(expression + offset)
    209        return [expression]
    210
    211    return expressions

Applies an offset to a given integer literal expression.

###### Arguments:

- this: The target of the index.
- expressions: The expression the offset will be applied to, wrapped in a list.
- offset: The offset that will be applied.
- dialect: the dialect of interest.

###### Returns:

> The original expression with the offset applied to it, wrapped in a list. If the provided `expressions` argument contains more than one expression, it's returned unaffected.

def camel_to_snake_case(name: str) -> str: View Source

    214def camel_to_snake_case(name: str) -> str:
    215    """Converts `name` from camelCase to snake_case and returns the result."""
    216    return CAMEL_CASE_PATTERN.sub("_", name).upper()

Converts `name` from camelCase to snake_case and returns the result.

def while_changing( expression: sqlglot.expressions.Expression, func: Callable[[ sqlglot.expressions.Expression ], ~E]) -> ~E: View Source

    219def while_changing(expression: Expression, func: t.Callable[[Expression], E]) -> E:
    220    """
    221    Applies a transformation to a given expression until a fix point is reached.
    222
    223    Args:
    224        expression: The expression to be transformed.
    225        func: The transformation to be applied.
    226
    227    Returns:
    228        The transformed expression.
    229    """
    230    end_hash: t.Optional[int] = None
    231
    232    while True:
    233        # No need to walk the AST– we've already cached the hashes in the previous iteration
    234        if end_hash is None:
    235            for n in reversed(tuple(expression.walk())):
    236                n._hash = hash(n)
    237
    238        start_hash = hash(expression)
    239        expression = func(expression)
    240
    241        expression_nodes = tuple(expression.walk())
    242
    243        # Uncache previous caches so we can recompute them
    244        for n in reversed(expression_nodes):
    245            n._hash = None
    246            n._hash = hash(n)
    247
    248        end_hash = hash(expression)
    249
    250        if start_hash == end_hash:
    251            # ... and reset the hash so we don't risk it becoming out of date if a mutation happens
    252            for n in expression_nodes:
    253                n._hash = None
    254
    255            break
    256
    257    return expression

Applies a transformation to a given expression until a fix point is reached.

###### Arguments:

- expression: The expression to be transformed.
- func: The transformation to be applied.

###### Returns:

> The transformed expression.

def tsort(dag: Dict[~T, Set[~T]]) -> List[~T]: View Source

    260def tsort(dag: t.Dict[T, t.Set[T]]) -> t.List[T]:
    261    """
    262    Sorts a given directed acyclic graph in topological order.
    263
    264    Args:
    265        dag: The graph to be sorted.
    266
    267    Returns:
    268        A list that contains all of the graph's nodes in topological order.
    269    """
    270    result = []
    271
    272    for node, deps in tuple(dag.items()):
    273        for dep in deps:
    274            if dep not in dag:
    275                dag[dep] = set()
    276
    277    while dag:
    278        current = {node for node, deps in dag.items() if not deps}
    279
    280        if not current:
    281            raise ValueError("Cycle error")
    282
    283        for node in current:
    284            dag.pop(node)
    285
    286        for deps in dag.values():
    287            deps -= current
    288
    289        result.extend(sorted(current))  # type: ignore
    290
    291    return result

Sorts a given directed acyclic graph in topological order.

###### Arguments:

- dag: The graph to be sorted.

###### Returns:

> A list that contains all of the graph's nodes in topological order.

def open_file(file_name: str) -> <class 'TextIO'>: View Source

    294def open_file(file_name: str) -> t.TextIO:
    295    """Open a file that may be compressed as gzip and return it in universal newline mode."""
    296    with open(file_name, "rb") as f:
    297        gzipped = f.read(2) == b"\x1f\x8b"
    298
    299    if gzipped:
    300        import gzip
    301
    302        return gzip.open(file_name, "rt", newline="")
    303
    304    return open(file_name, encoding="utf-8", newline="")

Open a file that may be compressed as gzip and return it in universal newline mode.

@contextmanager
def csv_reader(read_csv: sqlglot.expressions.ReadCSV ) -> Any: View Source

    307@contextmanager
    308def csv_reader(read_csv: exp.ReadCSV) -> t.Any:
    309    """
    310    Returns a csv reader given the expression `READ_CSV(name, ['delimiter', '|', ...])`.
    311
    312    Args:
    313        read_csv: A `ReadCSV` function call.
    314
    315    Yields:
    316        A python csv reader.
    317    """
    318    args = read_csv.expressions
    319    file = open_file(read_csv.name)
    320
    321    delimiter = ","
    322    args = iter(arg.name for arg in args)  # type: ignore
    323    for k, v in zip(args, args):
    324        if k == "delimiter":
    325            delimiter = v
    326
    327    try:
    328        import csv as csv_
    329
    330        yield csv_.reader(file, delimiter=delimiter)
    331    finally:
    332        file.close()

Returns a csv reader given the expression `READ_CSV(name, ['delimiter', '|', ...])`.

###### Arguments:

- read_csv: A `ReadCSV` function call.

###### Yields:

> A python csv reader.

def find_new_name(taken: Collection[str], base: str) -> str: View Source

    335def find_new_name(taken: t.Collection[str], base: str) -> str:
    336    """
    337    Searches for a new name.
    338
    339    Args:
    340        taken: A collection of taken names.
    341        base: Base name to alter.
    342
    343    Returns:
    344        The new, available name.
    345    """
    346    if base not in taken:
    347        return base
    348
    349    i = 2
    350    new = f"{base}_{i}"
    351    while new in taken:
    352        i += 1
    353        new = f"{base}_{i}"
    354
    355    return new

Searches for a new name.

###### Arguments:

- taken: A collection of taken names.
- base: Base name to alter.

###### Returns:

> The new, available name.

def is_int(text: str) -> bool: View Source

    358def is_int(text: str) -> bool:
    359    return is_type(text, int)

def is_float(text: str) -> bool: View Source

    362def is_float(text: str) -> bool:
    363    return is_type(text, float)

def is_type(text: str, target_type: Type) -> bool: View Source

    366def is_type(text: str, target_type: t.Type) -> bool:
    367    try:
    368        target_type(text)
    369        return True
    370    except ValueError:
    371        return False

def name_sequence(prefix: str) -> Callable[[], str]: View Source

    374def name_sequence(prefix: str) -> t.Callable[[], str]:
    375    """Returns a name generator given a prefix (e.g. a0, a1, a2, ... if the prefix is "a")."""
    376    sequence = count()
    377    return lambda: f"{prefix}{next(sequence)}"

Returns a name generator given a prefix (e.g. a0, a1, a2, ... if the prefix is "a").

def object_to_dict(obj: Any, **kwargs) -> Dict: View Source

    380def object_to_dict(obj: t.Any, **kwargs) -> t.Dict:
    381    """Returns a dictionary created from an object's attributes."""
    382    return {
    383        **{k: v.copy() if hasattr(v, "copy") else copy(v) for k, v in vars(obj).items()},
    384        **kwargs,
    385    }

Returns a dictionary created from an object's attributes.

def split_num_words( value: str, sep: str, min_num_words: int, fill_from_start: bool = True) -> List[Optional[str]]: View Source

    388def split_num_words(
    389    value: str, sep: str, min_num_words: int, fill_from_start: bool = True
    390) -> t.List[t.Optional[str]]:
    391    """
    392    Perform a split on a value and return N words as a result with `None` used for words that don't exist.
    393
    394    Args:
    395        value: The value to be split.
    396        sep: The value to use to split on.
    397        min_num_words: The minimum number of words that are going to be in the result.
    398        fill_from_start: Indicates that if `None` values should be inserted at the start or end of the list.
    399
    400    Examples:
    401        >>> split_num_words("db.table", ".", 3)
    402        [None, 'db', 'table']
    403        >>> split_num_words("db.table", ".", 3, fill_from_start=False)
    404        ['db', 'table', None]
    405        >>> split_num_words("db.table", ".", 1)
    406        ['db', 'table']
    407
    408    Returns:
    409        The list of words returned by `split`, possibly augmented by a number of `None` values.
    410    """
    411    words = value.split(sep)
    412    if fill_from_start:
    413        return [None] * (min_num_words - len(words)) + words
    414    return words + [None] * (min_num_words - len(words))

Perform a split on a value and return N words as a result with `None` used for words that don't exist.

###### Arguments:

- value: The value to be split.
- sep: The value to use to split on.
- min_num_words: The minimum number of words that are going to be in the result.
- fill_from_start: Indicates that if `None` values should be inserted at the start or end of the list.

###### Examples:

>     >>> split_num_words("db.table", ".", 3)
>     [None, 'db', 'table']
>     >>> split_num_words("db.table", ".", 3, fill_from_start=False)
>     ['db', 'table', None]
>     >>> split_num_words("db.table", ".", 1)
>     ['db', 'table']

###### Returns:

> The list of words returned by `split`, possibly augmented by a number of `None` values.

def is_iterable(value: Any) -> bool: View Source

    417def is_iterable(value: t.Any) -> bool:
    418    """
    419    Checks if the value is an iterable, excluding the types `str` and `bytes`.
    420
    421    Examples:
    422        >>> is_iterable([1,2])
    423        True
    424        >>> is_iterable("test")
    425        False
    426
    427    Args:
    428        value: The value to check if it is an iterable.
    429
    430    Returns:
    431        A `bool` value indicating if it is an iterable.
    432    """
    433    from sqlglot import Expression
    434
    435    return hasattr(value, "__iter__") and not isinstance(value, (str, bytes, Expression))

Checks if the value is an iterable, excluding the types `str` and `bytes`.

###### Examples:

>     >>> is_iterable([1,2])
>     True
>     >>> is_iterable("test")
>     False

###### Arguments:

- value: The value to check if it is an iterable.

###### Returns:

> A `bool` value indicating if it is an iterable.

def flatten(values: Iterable[Union[Iterable[Any], Any]]) -> Iterator[Any]: View Source

    438def flatten(values: t.Iterable[t.Iterable[t.Any] | t.Any]) -> t.Iterator[t.Any]:
    439    """
    440    Flattens an iterable that can contain both iterable and non-iterable elements. Objects of
    441    type `str` and `bytes` are not regarded as iterables.
    442
    443    Examples:
    444        >>> list(flatten([[1, 2], 3, {4}, (5, "bla")]))
    445        [1, 2, 3, 4, 5, 'bla']
    446        >>> list(flatten([1, 2, 3]))
    447        [1, 2, 3]
    448
    449    Args:
    450        values: The value to be flattened.
    451
    452    Yields:
    453        Non-iterable elements in `values`.
    454    """
    455    for value in values:
    456        if is_iterable(value):
    457            yield from flatten(value)
    458        else:
    459            yield value

Flattens an iterable that can contain both iterable and non-iterable elements. Objects of type `str` and `bytes` are not regarded as iterables.

###### Examples:

>     >>> list(flatten([[1, 2], 3, {4}, (5, "bla")]))
>     [1, 2, 3, 4, 5, 'bla']
>     >>> list(flatten([1, 2, 3]))
>     [1, 2, 3]

###### Arguments:

- values: The value to be flattened.

###### Yields:

> Non-iterable elements in `values`.

def dict_depth(d: Dict) -> int: View Source

    462def dict_depth(d: t.Dict) -> int:
    463    """
    464    Get the nesting depth of a dictionary.
    465
    466    Example:
    467        >>> dict_depth(None)
    468        0
    469        >>> dict_depth({})
    470        1
    471        >>> dict_depth({"a": "b"})
    472        1
    473        >>> dict_depth({"a": {}})
    474        2
    475        >>> dict_depth({"a": {"b": {}}})
    476        3
    477    """
    478    try:
    479        return 1 + dict_depth(next(iter(d.values())))
    480    except AttributeError:
    481        # d doesn't have attribute "values"
    482        return 0
    483    except StopIteration:
    484        # d.values() returns an empty sequence
    485        return 1

Get the nesting depth of a dictionary.

###### Example:

>     >>> dict_depth(None)
>     0
>     >>> dict_depth({})
>     1
>     >>> dict_depth({"a": "b"})
>     1
>     >>> dict_depth({"a": {}})
>     2
>     >>> dict_depth({"a": {"b": {}}})
>     3

def first(it: Iterable[~T]) -> ~T: View Source

    488def first(it: t.Iterable[T]) -> T:
    489    """Returns the first element from an iterable (useful for sets)."""
    490    return next(i for i in it)

Returns the first element from an iterable (useful for sets).

def to_bool(value: Union[str, bool, NoneType]) -> Union[str, bool, NoneType]: View Source

    493def to_bool(value: t.Optional[str | bool]) -> t.Optional[str | bool]:
    494    if isinstance(value, bool) or value is None:
    495        return value
    496
    497    # Coerce the value to boolean if it matches to the truthy/falsy values below
    498    value_lower = value.lower()
    499    if value_lower in ("true", "1"):
    500        return True
    501    if value_lower in ("false", "0"):
    502        return False
    503
    504    return value

def merge_ranges(ranges: List[Tuple[~A, ~A]]) -> List[Tuple[~A, ~A]]: View Source

    507def merge_ranges(ranges: t.List[t.Tuple[A, A]]) -> t.List[t.Tuple[A, A]]:
    508    """
    509    Merges a sequence of ranges, represented as tuples (low, high) whose values
    510    belong to some totally-ordered set.
    511
    512    Example:
    513        >>> merge_ranges([(1, 3), (2, 6)])
    514        [(1, 6)]
    515    """
    516    if not ranges:
    517        return []
    518
    519    ranges = sorted(ranges)
    520
    521    merged = [ranges[0]]
    522
    523    for start, end in ranges[1:]:
    524        last_start, last_end = merged[-1]
    525
    526        if start <= last_end:
    527            merged[-1] = (last_start, max(last_end, end))
    528        else:
    529            merged.append((start, end))
    530
    531    return merged

Merges a sequence of ranges, represented as tuples (low, high) whose values belong to some totally-ordered set.

###### Example:

>     >>> merge_ranges([(1, 3), (2, 6)])
>     [(1, 6)]

def is_iso_date(text: str) -> bool: View Source

    534def is_iso_date(text: str) -> bool:
    535    try:
    536        datetime.date.fromisoformat(text)
    537        return True
    538    except ValueError:
    539        return False

def is_iso_datetime(text: str) -> bool: View Source

    542def is_iso_datetime(text: str) -> bool:
    543    try:
    544        datetime.datetime.fromisoformat(text)
    545        return True
    546    except ValueError:
    547        return False

DATE_UNITS = {'year', 'year_month', 'month', 'week', 'day', 'quarter'}
def is_date_unit(expression: Optional[ sqlglot.expressions.Expression ]) -> bool: View Source

    554def is_date_unit(expression: t.Optional[exp.Expression]) -> bool:
    555    return expression is not None and expression.name.lower() in DATE_UNITS

class SingleValuedMapping(typing.Mapping[~K, ~V]): View Source

    562class SingleValuedMapping(t.Mapping[K, V]):
    563    """
    564    Mapping where all keys return the same value.
    565
    566    This rigamarole is meant to avoid copying keys, which was originally intended
    567    as an optimization while qualifying columns for tables with lots of columns.
    568    """
    569
    570    def __init__(self, keys: t.Collection[K], value: V):
    571        self._keys = keys if isinstance(keys, Set) else set(keys)
    572        self._value = value
    573
    574    def __getitem__(self, key: K) -> V:
    575        if key in self._keys:
    576            return self._value
    577        raise KeyError(key)
    578
    579    def __len__(self) -> int:
    580        return len(self._keys)
    581
    582    def __iter__(self) -> t.Iterator[K]:
    583        return iter(self._keys)

Mapping where all keys return the same value.

This rigamarole is meant to avoid copying keys, which was originally intended as an optimization while qualifying columns for tables with lots of columns.

SingleValuedMapping(keys: Collection[~K], value: ~V) View Source

    570    def __init__(self, keys: t.Collection[K], value: V):
    571        self._keys = keys if isinstance(keys, Set) else set(keys)
    572        self._value = value