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exprs.py
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import re
from typing import Optional, Pattern, Union
def compile(expr: "expr", flags: int = 0) -> Pattern[str]:
"""Compile a cursive_re expression to a real regular expression.
"""
return re.compile(str(expr), flags)
class expr:
def __add__(self, other: "expr") -> "expr":
return sequence(self) + other
def __or__(self, other: "expr") -> "expr":
if isinstance(other, alternative):
return alternative(self) | other
return alternative(self, other)
def __str__(self) -> str: # pragma: no cover
raise NotImplementedError("subclasses must implement __str__()")
class beginning_of_line(expr):
"""Matches the beginning of a line.
Examples:
>>> str(beginning_of_line())
'^'
"""
def __str__(self) -> str:
return "^"
class end_of_line(expr):
"""Matches the end of a line.
Examples:
>>> str(end_of_line())
'$'
"""
def __str__(self) -> str:
return "$"
class anything(expr):
"""Matches any character.
Examples:
>>> str(anything())
'.'
"""
def __str__(self) -> str:
return "."
class literal(expr):
"""Inserts a literal regular expression.
Examples:
>>> str(literal(r"\A\w"))
'\\\\A\\\\w'
"""
def __init__(self, literal: str) -> None:
self.literal = literal
def __str__(self) -> str:
return self.literal
class text(expr):
"""Matches the given string exactly, escaping any special characters.
Examples:
>>> str(text("abc"))
'abc'
"""
def __init__(self, text: str) -> None:
self.text = re.escape(text)
def __str__(self) -> str:
return self.text
class any_of(expr):
"""Matches any of the given characters.
Examples:
>>> str(any_of("ab"))
'[ab]'
>>> str(any_of(text("ab")))
'[ab]'
>>> str(any_of(text("[]")))
'[\\\\[\\\\]]'
"""
def __init__(self, e: Union[str, expr]) -> None:
self.expr = maybe_text(e)
def __str__(self) -> str:
return f"[{self.expr}]"
class none_of(expr):
"""Matches none of the given characters.
Examples:
>>> str(none_of("ab"))
'[^ab]'
>>> str(none_of(text("ab")))
'[^ab]'
>>> str(none_of(text("[]")))
'[^\\\\[\\\\]]'
"""
def __init__(self, e: Union[str, expr]) -> None:
self.expr = maybe_text(e)
def __str__(self) -> str:
return f"[^{self.expr}]"
class in_range(expr):
"""Matches a character in the given range.
Examples:
>>> str(in_range("a", "z"))
'a-z'
"""
def __init__(self, lo: str, hi: str) -> None:
self.lo = lo
self.hi = hi
def __str__(self) -> str:
return f"{self.lo}-{self.hi}"
class zero_or_more(expr):
"""Matches zero or more of the given expr.
Examples:
>>> str(zero_or_more("a"))
'(?:a)*'
>>> str(zero_or_more(text("a")))
'(?:a)*'
>>> str(zero_or_more(text("abc")))
'(?:abc)*'
>>> str(zero_or_more(group(text("abc"))))
'(abc)*'
"""
def __init__(self, e: Union[str, expr]) -> None:
self.expr = maybe_group(maybe_text(e))
def __str__(self) -> str:
return f"{self.expr}*"
class one_or_more(expr):
"""Matches one or more of the given expr.
Examples:
>>> str(one_or_more("a"))
'(?:a)+'
>>> str(one_or_more(text("a")))
'(?:a)+'
>>> str(one_or_more(group(text("abc"))))
'(abc)+'
"""
def __init__(self, e: Union[str, expr]) -> None:
self.expr = maybe_group(maybe_text(e))
def __str__(self) -> str:
return f"{self.expr}+"
class maybe(expr):
"""Matches an expr if present.
Examples:
>>> str(maybe("abc"))
'(?:abc)?'
>>> str(maybe(text("abc")))
'(?:abc)?'
>>> str(maybe(group(text("abc"))))
'(abc)?'
>>> str(maybe(any_of("abc")))
'[abc]?'
"""
def __init__(self, e: Union[str, expr]) -> None:
self.expr = maybe_group(maybe_text(e))
def __str__(self) -> str:
return f"{self.expr}?"
class repeated(expr):
"""Matches an expr repeated an exact number of times.
Examples:
>>> str(repeated("a", exactly=5))
'(?:a){5}'
>>> str(repeated(text("a"), exactly=5))
'(?:a){5}'
>>> str(repeated(text("a"), at_least=1))
'(?:a){1,}'
>>> str(repeated(text("a"), at_most=5))
'(?:a){0,5}'
>>> str(repeated(text("a"), at_least=2, at_most=5, greedy=False))
'(?:a){2,5}?'
"""
def __init__(
self, e: Union[str, expr], *,
exactly: Optional[int] = None,
at_least: int = 0,
at_most: Optional[int] = None,
greedy: bool = True,
) -> None:
self.expr = maybe_group(maybe_text(e))
self.exactly = exactly
self.at_least = at_least
self.at_most = at_most
self.greedy = greedy
def __str__(self) -> str:
if self.exactly is not None:
return f"{self.expr}{{{self.exactly}}}"
if self.at_most is not None:
expr = f"{self.expr}{{{self.at_least},{self.at_most}}}"
else:
expr = f"{self.expr}{{{self.at_least},}}"
if not self.greedy:
return f"{expr}?"
return expr
class alternative(expr):
"""Matches one of the given list of exprs.
"""
def __init__(self, *exprs: expr) -> None:
self.exprs = [maybe_group(e) for e in exprs]
def __or__(self, other: "expr") -> "expr":
if isinstance(other, alternative):
return alternative(*self.exprs, *other.exprs)
return alternative(*self.exprs, other)
def __str__(self) -> str:
return "|".join(str(expr) for expr in self.exprs)
class sequence(expr):
"""Groups the given set of exprs in order.
"""
def __init__(self, *exprs: expr) -> None:
self.exprs = exprs
def __add__(self, other: expr) -> expr:
if isinstance(other, sequence):
return sequence(*self.exprs, *other.exprs)
return sequence(*self.exprs, other)
def __str__(self) -> str:
return "".join(str(expr) for expr in self.exprs)
class group(expr):
"""Denotes a group whose contents can be retrieved after a match
is performed.
Examples:
>>> str(group(text("a")))
'(a)'
>>> str(group(any_of("abc"), name="chars"))
'(?P<chars>[abc])'
"""
def __init__(self, e: expr, *, name: Optional[str] = None, capture: bool = True) -> None:
assert isinstance(e, expr), "group must be passed an expr"
self.expr = e
self.name = name
self.capture = capture
def __str__(self) -> str:
if not self.capture:
return f"(?:{self.expr})"
if self.name is not None:
return f"(?P<{self.name}>{self.expr})"
return f"({self.expr})"
GROUPLIKES = (alternative, group, any_of, none_of)
def maybe_text(e: Union[str, expr]) -> expr:
return e if isinstance(e, expr) else text(e)
def maybe_group(e: expr) -> expr:
return e if isinstance(e, GROUPLIKES) else group(e, capture=False)