Get the first element after split

str.split finds all the occurrences of a separator and returns a list.

If you only need the first element then this is inefficient in two ways:

There's search for the separator beyond the first occurrence
The method returns all the other elements in the last which is not needed



In [1]:

    
def get_first_split(input_string, split_by=' '):
    try:
        input_string_stripped = input_string.strip()
        split_by_index = input_string_stripped.find(split_by)
        if split_by_index == -1:
            return input_string_stripped
        else:
            substring = input_string_stripped[:split_by_index].strip()
            return substring
    except AttributeError:
        return ''



In [2]:

    
get_first_split(' this is  _ a test', '_')









    Out[2]:





'this is'



In [3]:

    
get_first_split('some_group_1', '_')









    Out[3]:





'some'

Performance compared to `str.split`



In [8]:

    
x = 'XQWRQW' * 100000
x += ' ' + ('XWQQWFW' * 100000)



In [9]:

    
len(x)









    Out[9]:





1300001



In [46]:

    
%%timeit
x.split()[0]









    



1000 loops, best of 3: 1.43 ms per loop



In [12]:

    
%%timeit
x.split(maxsplit=1)[0]









    



1000 loops, best of 3: 700 µs per loop



In [47]:

    
%%timeit
get_first_split(x)









    



10000 loops, best of 3: 53.4 µs per loop

Get the first element after split

Performance compared to str.split

Performance compared to `str.split`