Skip to main content

Minify Python 2 source code

Project description

a Python 2 minifier by Gareth Rees <>


minipy is a minifier for Python 2. It rewrites Python 2 source code in a way that preserves the meaning of the code while reducing it in size. For example:

$ cat
cache = {0: 0, 1: 1, 2: 1, 3: 2}
def fibonacci(n):
    """Return the nth Fibonacci number."""
    if n not in cache:
        a = n // 2
        r = n % 2
        m = (r * 2) - 1
        cache[n] = fibonacci(a + 1) ** 2 + m * fibonacci(a + r - 1) ** 2
    return cache[n]

$ minipy --rename --docstrings
def c(a):
 if a not in b:d=a//2;e=a%2;f=e*2-1;b[a]=c(d+1)**2+f*c(d+e-1)**2
 return b[a]

Command line

Usage: minipy [options] [-o OUTPUT] FILE

  --version             show program's version number and exit
  -h, --help            show this help message and exit
  -o OUTPUT, --output=OUTPUT
                        output file (default: stdout)
  -D, --docstrings      remove docstrings and other statements with no side
                        effects (implies --noselftest)
  -R, --rename          aggressively rename non-preserved variables
  -i INDENT, --indent=INDENT
                        number of spaces per indentation level
  -p PRESERVE, --preserve=PRESERVE
                        preserve words from renaming (separate by commas)
  --nojoinlines         put each statement on its own line
  --noselftest          skip the self-test
  --debug               dump the parse tree

The self-test

Generating minified source code without accidentally changing the meaning is tricky: see the list of issues for many awkward cases that had to be fixed. Therefore, in its default operating mode, minipy performs a “self-test”: it takes the minified code, re-parses it, and asserts that the parse tree for the minified code is identical to the parse tree for the original code. If the self-test passes, then you can be highly confident that minipy has not changed the meaning of your code.

In order to pass the self-test, minipy must eschew a few changes to the code that result in harmless changes to the parse tree. These changes are:

  • Replacing pass with 0.
  • Replacing -(1) with -1.

You can use the --noselftest option to enable these changes, but by disabling the self-test you accept a small risk of a bug in minipy changing the meaning of your code.

The optional transformations --rename and --docstrings can’t be combined with the self-test, so these options imply --noselftest.

Please report all self-test failures, attaching the code that causes the failure.


Python’s use of introspection and duck typing means that it is not possible to change names in a program without risk of changing the meaning. The --rename option to minipy therefore makes a “best attempt” to discover names that need to be preserved, but does not guarantee anything. Use at your own risk!

The following names are preserved when renaming:

  • Names specified on the command-line via the --preserve option (write --preserve=name1,name2,name3 to preserve more than one name).
  • Built-in names (abs, all, any, apply, …).
  • Any name used as an attribute (.join, .index, .copy, .sort, …).
  • Any name starting and ending with two underscores.
  • The names of all imported modules.
  • Any name exported by a module in a from module import * statement.
  • Any name in the list assigned to the __all__ global variable.


minipy is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

Project details

Supported by

AWS AWS Cloud computing Datadog Datadog Monitoring Facebook / Instagram Facebook / Instagram PSF Sponsor Fastly Fastly CDN Google Google Object Storage and Download Analytics Huawei Huawei PSF Sponsor Microsoft Microsoft PSF Sponsor NVIDIA NVIDIA PSF Sponsor Pingdom Pingdom Monitoring Salesforce Salesforce PSF Sponsor Sentry Sentry Error logging StatusPage StatusPage Status page