How to change part of a variable (string)?

[IanJAl]

I have a variable "fileName" = ****.pdb, where the *s are capitalised letters. After a method uses this variable as an argument, I need to change the extension part to .ent without changing the first part. For some reason, none of the str.replace methods seem to work.

[dwblas]

none of the str.replace methods seem to work.

Yes they do. Post what you have tried and someone will tell you where you went wrong.

[Glenton]

If you know it's always that format you can just use:

newstring=fileName[:-3]+"ent"

[bvdet]

Keep in mind strings are immutable. You must reassign the string returned by the replace method to an identifier.

>>> s = "somestring.txt"
>>> s.replace("txt", "xyz")
'somestring.xyz'
>>> s
'somestring.txt'
>>> news = s.replace("txt", "xyz")
>>> news
'somestring.xyz'