How to make the tab character 4 spaces instead of 8 spaces in nano?

When I press TAB in nano editor, the cursor will jump with 8 spaces like this:

def square(x):
        return x * x
def cube(y):
        return y * y * y

how can I set the tab stop width to 4 spaces to display like this:

def square(x):
    return x * x
def cube(y):
    return y * y * y

If you use nano with a language like python (as in your example) it's also a good idea to convert tabs to spaces.

Edit your ~/.nanorc file (or create it) and add:

set tabsize 4
set tabstospaces

If you already got a file with tabs and want to convert them to spaces i recommend the expandcommand (shell):

expand -4 input.py > output.py

Command-line flag

From man nano:

-T cols (--tabsize=cols)
    Set the size (width) of a tab to cols columns.
    The value of cols must be greater than 0. The default value is 8.
-E (--tabstospaces)
    Convert typed tabs to spaces.

For example, to set the tab size to 4, replace tabs with spaces, and edit the file "foo.txt", you would run the command:

nano -ET4 foo.txt

Config file

From man nanorc:

set tabsize n
    Use a tab size of n columns. The value of n must be greater than 0.
    The default value is 8.
set/unset tabstospaces
    Convert typed tabs to spaces.

Edit your ~/.nanorc file (create it if it does not exist), and add those commands to it. For example:

set tabsize 4
set tabstospaces

Nano will use these settings by default whenever it is launched, but command-line flags will override them.

In nano 2.2.6 the line in ~/.nanorc to do this seems to be

set tabsize 4

Setting tabspace gave me the error: 'Unknown flag "tabspace"'

Setting the tab size in nano

cd /etc
ls -a
sudo nano nanorc

Link: https://app.gitbook.com/@cai-dat-chrome-ubuntu-18-04/s/chuaphanloai/setting-the-tab-size-in-nano

For future viewers, there is a line in my /etc/nanorc file close to line 153 that says "set tabsize 8". The word might need to be tabsize instead of tabspace. After I replaced 8 with 4 and uncommented the line, it solved my problem.