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Edit multiple files using Python text processing modules

Project Description


formerly known as Python Mass Editor

Implements a python mass editor to process text files using Python code. The modification(s) is (are) shown on stdout as a diff output. One can then modify the target file(s) in place with the -w/–write option. This is very similar to 2to3 tool that ships with Python 3.

WARNING: A word of caution about the usage of eval()

This tool is useful as far as it goes but it does rely on the python eval() function and does not check the code being executed. It is a major security risk and one should not use this tool in a production environment.

See Ned Batchelder’s article for a thorough discussion of the dangers linked to eval() and ways to circumvent them. Note that None of the counter-measure suggested in the article are implemented at this time.


You probably will need to know the basics of the Python re module (regular expressions).

usage: [-h] [-V] [-w] [-v] [-e EXPRESSIONS] [-f FUNCTIONS]
                   [-x EXECUTABLES] [-s START_DIRS] [-m MAX_DEPTH] [-o output]
                   pattern [pattern ...]

Python mass editor

positional arguments:
  pattern               shell-like file name patterns to process.

optional arguments:
  -h, --help            show this help message and exit
  -V, --version         show program's version number and exit
  -w, --write           modify target file(s) in place. Shows diff otherwise.
  -v, --verbose         increases log verbosity (can be specified multiple
                        Python expressions applied to target files. Use the
                        line variable to reference the current line.
  -f FUNCTIONS, --function FUNCTIONS
                        Python function to apply to target file. Takes file
                        content as input and yield lines. Specify function as
                        [module]:?<function name>.
                        Python executable to apply to target file.
                        Directory(ies) from which to look for targets.
  -m MAX_DEPTH, --max-depth-level MAX_DEPTH
                        Maximum depth when walking subdirectories.
  -o FILE, --output FILE
                        redirect output to a file
  -g FILE, --generate FILE
                        generate input file suitable for -f option
  --encoding ENCODING   Encoding of input and output files

# Simple string substitution (-e). Will show a diff. No changes applied. -e "re.sub('failIf', 'assertFalse', line)" *.py

# File level modifications (-f). Overwrites the files in place (-w). -w -f fixer:main *.py

# Will change all test*.py in subdirectories of tests. -e "re.sub('failIf', 'assertFalse', line)" -s tests test*.py

If massedit is installed as a package (from pypi for instance), one can interact with it as a command line tool:

python -m massedit -e "re.sub('assertEquals', 'assertEqual', line)"

Or as a library (command line option above to be passed as kewyord arguments):

>>> import massedit
>>> filenames = ['']
>>> massedit.edit_files(filenames, ["re.sub('Jerome', 'J.', line)"])

Lastly, there is a convenient massedit.bat wrapper for Windows included in the distribution.


Download from or :

pip install massedit

Poor man source-to-source manipulation

I find myself using massedit mostly for source to source modification of large code bases like this:

First create a python module with the function that will process your source code. For instance, to add a header:

def add_header(lines, file_name):
    yield '// This is my header'  # will be the first line of the file.
    for line in lines:
        yield line

Adds the location of to your $PYTHONPATH, then simply call like this: -f fixer:add_header *.h

You can add the -s . option to process all the .h files reccursively.


  • Add support for 3rd party tool (e.g. autopep8) to process the files.
  • Add support for a file of expressions as an argument to allow multiple modification at once.
  • Find a satisfactory way (ie. easy to use) to handle multiline regex as the current version works on a line by line basis.


  • I have a hard time practicing more than a few dialects of regular expressions.
  • I need something portable to Windows without being bothered by eol.
  • I believe Python is the ideal tool to build something more powerful than simple regex based substitutions.


I have been using runsed and checksed (from Unix Power Tools) for years and did not find a good substitute under Windows until I came across Graham Fawcett python recipe 437932 on ActiveState. It inspired me to write the massedit.

The core was fleshed up a little, and here we are. If you find it useful and enhance it please, do not forget to submit patches. Thanks!

If you are more interested in awk-like tool, you probably will find pyp a better alternative. This is certainly a more mature tool.


Licensed under the term of MIT License. See attached file LICENSE.txt.


0.68.3 (2017-09-20)
Added –generate option to quickly generate a template file to be modified to be used with -f fixer.fixit option. Added official support for Python 3.6
0.68.1 (2016-06-04)
Fixed encoding issues when processing non-ascii files. Added –encoding option to force the value of the encoding if need be. Listed support for Python 3.5
0.67.1 (2015-06-28)
Documentation fixes.
0.67 (2015-06-23)
Added file_name argument to processing functions. Fixed incorrect closing of sys.stdout/stderr. Improved diagnostic when the processing function does not take 2 arguments. Swapped -v and -V option to be consistent with Python. Pylint fixes. Added support for Python 3.4. Dropped support for Python 3.2.
0.66 (2013-07-14)
Fixed lost executable bit with -f option (thanks myint).
0.65 (2013-07-12)
Added -f option to execute code in a separate file/module. Added Travis continuous integration (thanks myint). Fixed python 2.7 support (thanks myint).
0.64 (2013-06-01)
Fixed so that massedit installs as a script. Fixed eol issues (thanks myint).
0.63 (2013-05-27)
Renamed to massedit. Previous version are still known as Python-Mass-Editor.
0.62 (2013-04-11)
Fixed bug that caused an EditorError to be raised when the result of the expression is an empty string.
0.61 (2012-07-06)
Added massedit.edit_files function to ease usage as library instead of as a command line tool (suggested by Maxim Veksler).
0.60 (2012-07-04)
Treats arguments as patterns rather than files to ease processing of multiple files in multiple subdirectories. Added -s (start directory) and -m (max depth) options.
0.52 (2012-06-05)
Upgraded for python 3. Still compatible with python 2.7.
0.51 (2012-05)
Initial release (Beta).

Contributor acknowledgement

Steven Myint,

Release History

Release History

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