I have some Python code that have inconsistent indentation. There is a lot of mixture of tabs and spaces to make the matter even worse, and even space indentation is not preserved.

The code works as expected, but it’s difficult to maintain.

How can I fix the indentation (like HTML Tidy, but for Python) without breaking the code?

Use the reindent.py script that you find in the Tools/scripts/ directory of your Python installation:

Change Python (.py) files to use 4-space indents and no hard tab characters. Also trim excess spaces and tabs from ends of lines, and remove empty lines at the end of files. Also ensure the last line ends with a newline.

Have a look at that script for detailed usage instructions.

If you’re using Vim, see :h retab.

                                                        *:ret* *:retab*
:[range]ret[ab][!] [new_tabstop]
                        Replace all sequences of white-space containing a
                        <Tab> with new strings of white-space using the new
                        tabstop value given.  If you do not specify a new
                        tabstop size or it is zero, Vim uses the current value
                        of 'tabstop'.
                        The current value of 'tabstop' is always used to
                        compute the width of existing tabs.
                        With !, Vim also replaces strings of only normal
                        spaces with tabs where appropriate.
                        With 'expandtab' on, Vim replaces all tabs with the
                        appropriate number of spaces.
                        This command sets 'tabstop' to the new value given,
                        and if performed on the whole file, which is default,
                        should not make any visible change.
                        Careful: This command modifies any <Tab> characters
                        inside of strings in a C program.  Use "\t" to avoid
                        this (that's a good habit anyway).
                        ":retab!" may also change a sequence of spaces by
                        <Tab> characters, which can mess up a printf().
                        {not in Vi}
                        Not available when |+ex_extra| feature was disabled at
                        compile time.

For example, if you simply type

:ret

all your tabs will be expanded into spaces.

You may want to

:se et  " shorthand for :set expandtab

to make sure that any new lines will not use literal tabs.

If you’re not using Vim,

perl -i.bak -pe "s/\t/' 'x(8-pos()%8)/eg" file.py

will replace tabs with spaces, assuming tab stops every 8 characters, in file.py (with the original going to file.py.bak, just in case). Replace the 8s with 4s if your tab stops are every 4 spaces instead.

I would reach for autopep8 to do this:

$ # see what changes it would make
$ autopep8 path/to/file.py --select=E101,E121 --diff

$ # make these changes
$ autopep8 path/to/file.py --select=E101,E121 --in-place

Note: E101 and E121 are pep8 indentation (I think you can simply pass --select=E1 to fix all indentation related issues – those starting with E1).

You can apply this to your entire project using recursive flag:

$ autopep8 package_dir --recursive --select=E101,E121 --in-place

See also Tool to convert Python code to be PEP8 compliant.

autopep8 -i script.py

Use autopep8

autopep8 automagically formats Python code to conform to the PEP 8 nullstyle guide. It uses the pep8 utility to determine what parts of the nullcode needs to be formatted. autopep8 is capable of fixing most of the nullformatting issues that can be reported by pep8.

pip install autopep8
autopep8 script.py    # print only
autopep8 -i script.py # write file

Using Vim, it shouldn’t be more involved than hitting Esc, and then typing…

:%s/\t/    /g

…on the file you want to change. That will convert all tabs to four spaces. If you have inconsistent spacing as well, then that will be more difficult.

There is also PythonTidy (since you said you like HTML Tidy).

It can do a lot more than just clean up tabs though. If you like that type of thing, it’s worth a look.

On most UNIX-like systems, you can also run:

expand -t4 oldfilename.py > newfilename.py

from the command line, changing the number if you want to replace tabs with a number of spaces other than 4. You can easily write a shell script to do this with a bunch of files at once, retaining the original file names.

If you’re lazy (like me), you can also download a trial version of Wingware Python IDE, which has an auto-fix tool for messed up indentation. It works pretty well. http://www.wingware.com/

The reindent script did not work for me, due to some missing module. Anyway, I found this sed command which does the job perfect for me:

sed -r 's/^([  ]*)([^ ])/\1\1\2/' file.py

Try Emacs. It has good support for indentation needed in Python. Please check this link http://python.about.com/b/2007/09/24/emacs-tips-for-python-programmers.htm

Try IDLE, and use Alt + X to find indentation.

I have a simple solution for this problem. You can first type “:retab” and then “:retab!”, then everything would be fine

In case of trying to find tool to make your 2-space indented python script to a tab indented version, just use this online tool:

https://www.tutorialspoint.com/online_python_formatter.htm