Python - How to return the position in string where character matches from a list [duplicate]

Question

I have a list:

symbol_list = ['/', '.', '\"', '-']

and a changing string which currently contains:

string = 'This is a string/ of "text"'

and I'm trying to find the most efficient way to return the index value where the first match from the list is made in the string. e.g. index value is 16 in above example.

Any advice please?

Answer 1

First, make your symbol list a set for O(1) containment checks. Then use a generator and get its first value. I recommend -1 as the fallback value.

>>> symbol_list = ['/', '.', '\"', '-']
>>> symbol_set = set(symbol_list)
>>> string = 'This is a string/ of "text"'
>>> idx = next((idx for idx, c in enumerate(string) if c in symbol_set), -1)
>>> idx
16

Answer 2

You can iterate over the (index, character) pairs with enumerate(), and use a set for fast lookup:

>>> def get_pos(s):
...     for i, c in enumerate(s):
...         if c in {'/', '.', '\"', '-'}:
...             return i
... 
>>> s = 'This is a string/ of "text"'
>>> get_pos(s)
16

Answer 3

pattern = re.compile('['+"".join(symbol_list)+']')
print string.index(pattern.search(string).group())

Answer 4

Try this :

(i for i,c in enumerate(string) if c in symbol_list ).next()