I am trying to extract certain part of some strings. These strings look like

a = "1_2_3"
b = "1_2_3_4"

I would want to get everything of each string before the last underscore so:

"1_2"
"1_2_3"

I thought this line should work:

"_".join(a.split("_")[:-1])
"_".join(b.split("_")[:-1])

but it gives me the error: AttributeError: 'str' object has no attribute 'joint'

However, apparently, a.split("_")[:-1] is not a str but a list (I checked by type(a.split("_")[:-1])). Does anyone know why this happens and how to solve it?

CodePudding user response：

Sounds like you misspelled using str.join() as str.joint().

For your usecase though, looks like str.rpartition() would fit better, removing the split-join loop.

a = "1_2_3"
b = "1_2_3_4"

print(a.rpartition("_")[0])
print(b.rpartition("_")[0])

Output

1_2
1_2_3

CodePudding user response：

You got a good answer that addresses your problem that you should probably accept. But in case you want an alternative, you can make a slice of the string directly:

a = "1_2_3"
b = "1_2_3_4"

a[:a.rindex('_')]
# '1_2'

b[:b.rindex('_')]
# '1_2_3'

This works by finding the right-most index of _ in the string and slicing to that point.

CodePudding user response：

Or you could try rsplit:

>>> a = "1_2_3"
>>> x, _ = a.rsplit('_', 1)
>>> x
'1_2'
>>> 

Or one with regex:

>>> import re
>>> a = "1_2_3"
>>> re.sub('_\d$', '', a)
'1_2'
>>>