rgx 1.0.1

Typed, simple and readable regexp generation

Many people complain about unreadable and complex syntax of regular expressions.
Many others complain about how they can't remember all constructs and features.

rgx solves those problems: it is a straightforward regexp builder. It also places parens where needed to respect intended operator priority.
It can produce a regular expression string to use in re.compile or any other regex library of your choice.

Installation

pip install rgx

That's it.

Quickstart

in this readme, x means some pattern object. Occaasionaly, y is introduced to mean some other pattern object (or literal)

rgx operates mostly on so-called "pattern objects" — rgx.entities.RegexPattern istances.
Your starting point would be rgx.pattern — it creates pattern objects from literals (or from pattern objects which doesn't make a lot of sense).

• rgx.pattern(str, escape: bool = True) creates a literal pattern — one that exactly matches given string. If you want to disable escaping, pass escape=False
• rgx.pattern(tuple[AnyRegexPattern]) creates a non-capturing group of patterns (nested literals will be converted too)
• rgx.pattern(list[str]) creates a character class (for example, rgx.pattern(["a", "b", "c"]) creates pattern [abc], that matches any character of those in brackets)

Most operations with pattern objects support using Python literals on one side, for example: rgx.pattern("a") | b would produce a|b pattern object (specifically, rgx.entities.Option)

To render pattern, use either x.render_str(flags: str) or str(x). The only difference is that you can't pass regex flags into str().

To create a capturing group, use x.capture(), or rgx.reference(group: int) for a named reference.
To create a named capturing group, use rgx.named(name: str, x), or rgx.named(name: str) for a named reference.

For character ranges ([a-z]), use rgx.char_range(start?: str, stop?: str).
Multiple character classes can be combined with |: (rgx.char_range("a", "z")) | rgx.pattern(["1", "2", "3"]) -> [a-z123]
To reverse character class ([a-z123] -> [^a-z123]), use x.reverse() (works only on character classes).

For a conditional pattern, use rgx.conditional(group: int, x, y) (where x matches if group has matched, and y otherwise)

Basic usage

Hello, regex world

import rgx
import re

word = rgx.meta.WORD_CHAR.many().capture() # (\w+), a capturing group
comma = rgx.pattern(",").maybe()

regex = rgx.pattern((
    "hello",
    comma,
    rgx.meta.WHITESPACE,
    (
        word + rgx.meta.WHITESPACE
    ).maybe(),
    "world"
)) # (?:hello,?\s(?:(\w*)\s)?world)

re.compile(
    regex.render_str("i") # global flag (case-insensitive)
)

Match some integers

this regex will match valid Python integer literals:

import rgx
import re

nonzero = rgx.char_range("1", "9") # [1-9]
zero = "0"
digit = zero | nonzero # 0|[1-9]
integer = zero | (nonzero + digit.some()) # 0|[1-9](?:0|[1-9])*

int_regex = re.compile(str(integer))

...or this one:

import rgx
import re

nonzero = rgx.char_range("1", "9") # [1-9]
digit = rgx.meta.DIGIT # \d
integer = digit | (nonzero + digit.some()) # \d|[1-9]\d*

int_regex = re.compile(str(integer))

Docs

Pattern methods

pattern.render_str(flags: str = '') -> str

Renders given pattern into a string with specified global flags.

---

pattern.set_flags(flags: str) -> LocalFlags

This method adds local flags to given pattern

Render:

x.flags("y") # "(?y:x)"

---

pattern.concat(other: AnyRegexPattern) -> Concat

Use to match one pattern and then another.

A.concat(B) is equivalent to A + B (works if either A or B is a RegexPart object, not a Python literal)

Render:

x.concat(y) # "xy"
x + y # "xy"

---

pattern.option(other: AnyRegexPattern) -> Option

Use to match either one pattern or another.

A.option(B) is equivalent to A | B (if either A or B is a RegexPart object, not a Python literal)

Render:

x.option(y) # "x|y"
x | y # "x|y"

---

pattern.many(lazy: bool = False) -> Many

Use this for repeating patterns (one or more times)

When not lazy, matches as many times as possible, otherwise matches as few times as possible.

Render:

x.many() # "x+"
x.many(True) # "x+?"

---

pattern.some(lazy: bool = False) -> Some

Use this for repeating optional patterns (zero or more times)

When not lazy, matches as many times as possible, otherwise matches as few times as possible.

Render:

x.some() # "x*"
x.some(True) # "x*?"

---

pattern.maybe(lazy: bool = False) -> Maybe

Use this for optional patterns (zero or one times)

When not lazy, matches as many times as possible, otherwise matches as few times as possible.

Render:

x.maybe() # "x?"
x.maybe(True) # "x??"

---

pattern.x_or_less_times(count: int, lazy: bool = False) -> Range

Use this to match pattern x or less times (hence the name).

When not lazy, matches as many times as possible, otherwise matches as few times as possible.

Render:

x.x_or_less_times(5) # "x{,5}"
x.x_or_less_times(5, True) # "x{,5}?"

---

pattern.x_or_more_times(count: int, lazy: bool = False) -> Range

Use this to match pattern x or more times (hence the name).

When not lazy, matches as many times as possible, otherwise matches as few times as possible.

Render:

x.x_or_more_times(5) # "x{5,}"
x.x_or_more_times(5, True) # "x{5,}?"

---

pattern.x_times(count: int, lazy: bool = False) -> Range

Use this to match pattern exactly x times (hence the name).

When not lazy, matches as many times as possible, otherwise matches as few times as possible.

Render:

x.x_times(5) # "x{5}"
x.x_times(5, True) # "x{5}?"

---

pattern.between_x_y_times(min_count: int, max_count: int, lazy: bool = False) -> Range

Use this to match pattern between x and y times, inclusive (hence the name).

When not lazy, matches as many times as possible, otherwise matches as few times as possible.

Render:

x.between_x_y_times(5, 6) # "x{5,6}"
x.between_x_y_times(5, 6, True) # "x{5,6}?"

---

pattern.lookahead(other: RegexPattern) -> Concat

Use this to indicate that given pattern occurs before some another pattern (lookahead).

In other words, x.lookahead(y) matches a pattern x only if there is y after it

Lookahead pattern won't be captured.

Render:

x.lookahead(y) # x(?=y)
x.before(y) # x(?=y)

---

pattern.negative_lookahead(other) -> Concat

Use this to indicate that given pattern doesn't occur before some another pattern (negative lookahead).

In other words, x.negative_lookahead(y) matches a pattern x only if there is no y after it

Lookahead pattern won't be captured.

Render:

x.negative_lookahead(y) # x(?!y)
x.not_before(y) # x(?!y)

---

pattern.lookbehind(other: RegexPattern) -> Concat

Use this to indicate that given pattern occurs after some another pattern (lookahead).

In other words, x.lookbehind(y) matches a pattern x only if there is y before it

Lookbehind pattern won't be captured.

Render:

x.lookbehind(y) # (?<=y)x
x.after(y) # (?<=y)x

---

pattern.negative_lookbehind(other) -> Concat

Use this to indicate that given pattern goes before some another pattern (lookahead).

In other words, x.negative_lookbehind(y) matches a pattern x only if there is NO y before it

Lookbehind pattern won't be captured.

Render:

x.negative_lookbehind(y) # (?<!y)x
x.not_after(y) # (?<!y)x

---

pattern.capture() -> Group

Use this to make a capturing group out of pattern.

Render:

x.capture() # (x)

Common questions

Difference between (x, y) and x + y

Previous examples used () and +, and the difference might not be so obvious.

• x + y creates a concatenation of patterns (rgx.entities.Concat), with no extra characters apart from those of patterns

• x + y can be used only if at least one of the operands is a pattern object (that is, created with one of rgx functions or is one of rgx constants)

• x + y produces a pattern object itself, so you won't need to call pattern on it to call pattern methods

• pattern((x, y)) creates a non-capturing group (rgx.entities.NonCapturingGroup): pattern((x, y)).render_str() -> (?:xy)

• (x, y) can be used with any pattern-like literals or pattern objects

• (x, y) is a tuple literal, so you can't use pattern methods on it directly or convert it into a complete expression (you need to use rgx.pattern on it first)