CODEWITHSUNDEEP
pythonlistloops
Megan
Megan

Reputation: 205

python: loop through list of strings find index of specified element

I'm sure this is simple and I'm looking right at it, but I cannot make it work.

Goal: Use a loop to go through the list of strings and find the search term. Return the element number of the first match.

I've tried a few options, nothing seems to work, and I have yet to find a working description of how to do it in any texts.

This is my best attempt so far: 

def get_element_number(a_list, search_term):
    for i in range(len(a_list)):
      if search_term in a_list[i]:
        return a_list.index(i)
      elif not search_term in a_list:
        return 'no match'

Error message:

Traceback (most recent call last):
File "python", line 11, in <module>
File "python", line 5, in get_element_number
ValueError: 2 is not in list

Not looking for the complete answer, just any help in where I'm going wrong or if I'm missing something would be very helpful.

Upvotes: 2

Views: 6073

Answers (6)

Krzysiek Kowalski
Krzysiek Kowalski

Reputation: 72

def find_element(a_list, search_term):
i = 0
for e in a_list:
    if e == search_term:
        return i
    i += 1
return -1

Very nice explanation for either this one or other solution you can find in the video linked below

https://www.youtube.com/watch?time_continue=216&v=GwOFHuPMCpM

Upvotes: 0

Taufiq Rahman
Taufiq Rahman

Reputation: 5714

Here's a simple change to your code that will resolve it:

def get_element_number(a_list, search_term):
    if search_term in a_list: #if search keyword is in the list
        return a_list.index(search_term) #then return the index of that
    else:
        return 'no match!'

Upvotes: 0

宏杰李
宏杰李

Reputation: 12168

def get_element_number(a_list, search_term):
    for index, value in enumerate(a_list):
        if search_term in value:
            return index
    return 'not match'

Upvotes: 0

Hanan
Hanan

Reputation: 1445

for index, s in enumerate(a_list):
  if s == term:
    return index
return -1

Upvotes: 0

Roel Strolenberg
Roel Strolenberg

Reputation: 2950

You can replace all of this with index = a_list.index(search_term).

Note that if the list doesn't contain the search_term, it will throw an exception, so you'll need to catch that and return "not found" or something similar. Second note: it only returns the first index of the found search_term.

Upvotes: 3

Jean-Fran&#231;ois Fabre
Jean-Fran&#231;ois Fabre

Reputation: 140256

if search_term in a_list[i]: is True even if search_term is contained in a_list[i].

So in the case of an exact match index works, but in a case of a partial match index throws an exception.

Aside: elif not search_term in a_list: is wrong. Remove it or you'll return at first non-match.

Rewrite it as:

def get_element_number(a_list, search_term):
     try:
          return a_list.index(search_term)
     except IndexError:
          'no match'

This is simpler and has the advantage of performing search only once, which is important performance-wise when you're using linear search (not taking the overhead of exception into account).

Upvotes: 3

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