How to get the position of a character in Python?

There are two string methods for this, find() and index(). The difference between the two is what happens when the search string isn't found. find() returns -1 and index() raises a ValueError.

Using find()

>>> myString = 'Position of a character'
>>> myString.find('s')
2
>>> myString.find('x')
-1

Using index()

>>> myString = 'Position of a character'
>>> myString.index('s')
2
>>> myString.index('x')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: substring not found

From the Python manual

string.find(s, sub[, start[, end]])
Return the lowest index in s where the substring sub is found such that sub is wholly contained in s[start:end]. Return -1 on failure. Defaults for start and end and interpretation of negative values is the same as for slices.

And:

string.index(s, sub[, start[, end]])
Like find() but raise ValueError when the substring is not found.

Just for a sake of completeness, if you need to find all positions of a character in a string, you can do the following:

s = 'shak#spea#e'
c = '#'
print([pos for pos, char in enumerate(s) if char == c])

which will print: [4, 9]

>>> s="mystring"
>>> s.index("r")
4
>>> s.find("r")
4

"Long winded" way

>>> for i,c in enumerate(s):
...   if "r"==c: print i
...
4

to get substring,

>>> s="mystring"
>>> s[4:10]
'ring'

Just for completion, in the case I want to find the extension in a file name in order to check it, I need to find the last '.', in this case use rfind:

path = 'toto.titi.tata..xls'
path.find('.')
4
path.rfind('.')
15

in my case, I use the following, which works whatever the complete file name is:

filename_without_extension = complete_name[:complete_name.rfind('.')]