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Bracex

Overview

Bracex is a brace expanding library (à la Bash) for Python. Brace expanding is used to generate arbitrary strings.

$ echo {{a,b},c}d
ad bd cd

Bracex adds this ability to Python:

>>> bracex.expand(r'file-{1,2,3}.txt')
['file-1.txt', 'file-2.txt', 'file-3.txt']

and as a command:

$ python3 -m bracex -0 "base/{a,b}/{1..2}" | xargs -0 mkdir -p
$ tree base/
base/
├── a
│   ├── 1
│   └── 2
└── b
    ├── 1
    └── 2

  • Why Bracex over other solutions?

    Bracex actually follows pretty closely to how Bash processes braces. It is not a 1:1 implementation of how Bash handles braces, but generally, it follows very closely. Almost all of the test cases are run through Bash first, then our implementation is compared against the results Bash gives. There are a few cases where we have purposely deviated. For instance, we are not handling Bash's command line inputs, so we are not giving special meaning to back ticks and quotes at this time.

    On the command line Bracex can handle more expansions than Bash itself.

More Examples:

>>> bracex.expand(r'-v{,,}')
['-v', '-v', '-v']

Nested braces:

>>> bracex.expand(r'file-{{a,b},c}d.txt')
['file-ad.txt', 'file-bd.txt', 'file-cd.txt']

Numerical sequences:

>>> bracex.expand(r'file{0..3}.txt')
['file0.txt', 'file1.txt', 'file2.txt', 'file3.txt']

>>> bracex.expand(r'file{0..6..2}.txt')
['file0.txt', 'file2.txt', 'file4.txt', 'file6.txt']

>>> bracex.expand(r'file{00..10..5}.jpg')
['file00.jpg', 'file05.jpg', 'file10.jpg']

Alphabetic sequences:

>>> bracex.expand(r'file{A..D}.txt')
['fileA.txt', 'fileB.txt', 'fileC.txt', 'fileD.txt']

>>> bracex.expand(r'file{A..G..2}.txt')
['fileA.txt', 'fileC.txt', 'fileE.txt', 'fileG.txt']

Allows escaping:

>>> bracex.expand(r'file\{00..10..5}.jpg')
['file{00..10..5}.jpg']

>>> bracex.expand(r'file\{00..10..5}.jpg', keep_escapes=True)
['file\\{00..10..5}.jpg']

Bracex will not expand braces in the form of ${...}:

>>> bracex.expand(r'file${a,b,c}.jpg')
['file${a,b,c}.jpg']

Install

$ pip install bracex

API

expand()

def expand(string, keep_escapes=False, limit=1000):

expand accepts a string and returns a list of expanded strings. It will always return at least a single empty string [""]. By default, escapes will be resolved and the backslashes reduced accordingly, but keep_escapes will process the escapes without stripping them out.

By default, brace expansion growth is limited to 1000. This limit can be configured via the limit option. If you would like to remove the limit option, you simply set limit to 0.

iexpand()

def iexpand(string, keep_escapes=False, limit=1000):

iexpand is just like expand except it returns a generator.

Command line interface

$ python3 -m bracex --help
usage: python -mbracex [-h] [--terminator STR | -0] [--version] expression

Expands a bash-style brace expression, and outputs each expansion.

positional arguments:
  expression            Brace expression to expand

optional arguments:
  -h, --help            show this help message and exit
  --terminator STR, -t STR
                        Terminate each expansion with string STR (default: \n)
  -0                    Terminate each expansion with a NUL character
  --version             show program's version number and exit