Python Expand Tabs Length Calculation

Question

I'm confused by how the length of a string is calculated when expandtabs is used. I thought expandtabs replaces tabs with the appropriate number of spaces (with the default number of spaces per tab being 8). However, when I ran the commands using strings of varying lengths and varying numbers of tabs, the length calculation was different than I thought it would be (i.e., each tab didn't always result in the string length being increased by 8 for each instance of "/t").

Below is a detailed script output with comments explaining what I thought should be the result of the command executed above. Would someone please explain the how the length is calculated when expand tabs is used?

Click to copy

IDLE 2.6.5     
>>> s = '\t'
>>> print len(s)
1
>>> #the length of the string without expandtabs was one (1 tab counted as a single space), as expected.
>>> print len(s.expandtabs())
8
>>> #the length of the string with expandtabs was eight (1 tab counted as eight spaces).
>>> s = '\t\t'
>>> print len(s)
2
>>> #the length of the string without expandtabs was 2 (2 tabs, each counted as a single space).
>>> print len(s.expandtabs())
16
>>> #the length of the string with expandtabs was 16 (2 tabs counted as 8 spaces each).
>>> s = 'abc\tabc'
>>> print len(s)
7
>>> #the length of the string without expandtabs was seven (6 characters and 1 tab counted as a single space).
>>> print len(s.expandtabs())
11
>>> #the length of the string with expandtabs was NOT 14 (6 characters and one 8 space tabs).
>>> s = 'abc\tabc\tabc'
>>> print len(s)
11
>>> #the length of the string without expandtabs was 11 (9 characters and 2 tabs counted as a single space).
>>> print len(s.expandtabs())
19
>>> #the length of the string with expandtabs was NOT 25 (9 characters and two 8 space tabs).
>>>

Answer 1

Like when you are entering tabs in a text-editor, the tab character increases the length to the next multiple of 8.

So:

• '\t' by itself is 8, obviously.
• '\t\t' is 16.
• 'abc\tabc' starts at 3 characters, then a tab pushes it up to 8, and then the last 'abc' pushes it from 8 to 11...
• 'abc\tabc\tabc' likewise starts at 3, tab bumps it to 8, another 'abc' goes to 11, then another tab pushes it to 16, and the final 'abc' brings the length to 19.