Python 2 minifier
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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.
  • 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.