Find and print index of element in a list (string)

Question

I am trying to find an element in a list (string) and then print the index. Here is my code:

def checkLen():
days = ["Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday", "Sunday"]
position = 0
for i in days:
    if i == "Monday":
        position = i
        print("Found it")
        print(position)

But i am getting the result:

Found it
Monday

I have discovered that ,unlike other programming language that i know, Python variable type can change, which is why the Number type "position" changes to a "str", how do i save the index in position?

To use your code, you need to increment position within the loop. — user2963623
– user2963623, Commented Jul 8, 2014 at 10:06
One more way you can do this would be for i, day in enumerate(days): — karthikr
– karthikr, Commented Jul 8, 2014 at 13:44

lurknobserve · Accepted Answer · 2014-07-08 10:26:18Z

3

Lists have an index method that you can use

def checkLen(): 
     days = ["Monday", "Tuesday", "Wednesday", "Thursday" "Friday", "Saturday", "Sunday"]
     try:
         position = days.index("Monday")
         print("Found it") 
     except ValueError:
         position = None # or 0 if you want
         print("Not present") 
     print(position)

edited Jul 8, 2014 at 10:26

answered Jul 8, 2014 at 10:02

lurknobserve

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3 Comments

sundar nataraj Over a year ago

this will produce error if the monday not present in list

sundar nataraj Over a year ago

@OjonugwaOchalifu how you use else here.can you explain

Ojonugwa Jude Ochalifu Over a year ago

:D I was still referring to my original code.You sir,are correct.

unutbu · Accepted Answer · 2014-07-08 09:55:48Z

3

Use enumerate. It returns both the position and the item:

def checkLen():
    days = ["Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday", "Sunday"]
    for position, day in enumerate(days):
        if day == "Monday":
            print("Found it")
            print(position)

answered Jul 8, 2014 at 9:55

unutbu

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Comments

sundar nataraj · Accepted Answer · 2014-07-08 09:57:33Z

1

 def checkLen():
    days = ["Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday", "Sunday"]
    if "Monday" in days:
        print "found"
        print days.index("Monday")

you dont need to loop the days . just use in if it is found then index

answered Jul 8, 2014 at 9:57

sundar nataraj

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Comments

James Kent · Accepted Answer · 2014-07-08 10:19:25Z

1

there is an index function for lists:

days = ["Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday", "Sunday"]
print(days.index("Monday"))

note that this will raise an exception if the item is not in the list but will execute faster than looping over the list, especially if you have long lists.

however it will only give you the first index, so if there are duplicates you'll have to use other methods to find them.

a good resource for reading is http://effbot.org/zone/python-list.htm

as pointed out by Frerich Raabe in python most people tend to write code to assume that what you are looking for is there (ie the list has the element you are trying to find) and catch the exception raised if its not (exception raised is ValueError)

try not to use a general exception when you know the specific exception that should be raised as with more complex code it can make it harder to find other problems where another function call fails.

edited Jul 8, 2014 at 10:19

answered Jul 8, 2014 at 9:59

James Kent

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1 Comment

Frerich Raabe Over a year ago

I'd +1 this if you'd extend your answer to point out that in Python, people commonly "ask for forgiveness, not permission", i.e. you'd rather try to get the index and catch any error than to first check whether the element is contained.

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