You can do this using Python's slice notation:
>>> mystr = 'foo7bar'
>>> mystr[:mystr.index('7')]
'foo'
>>>
The format for slice notation is [start:stop:step]
. The index
method of a string finds the position of the first occurrence of its input.
Note however that if you are dealing with something more complex (such as matching patterns), you might want to look into Regular Expressions. For this operation though, the slice notation is sufficient.