If list index exists, do X

user_1569317 0
Viewed 393622

In my program, user inputs number n, and then inputs n number of strings, which get stored in a list.

I need to code such that if a certain list index exists, then run a function.

This is made more complicated by the fact that I have nested if statements about len(my_list).

Here's a simplified version of what I have now, which isn't working:

n = input ("Define number of actors: ")

count = 0

nams = []

while count < n:
    count = count + 1
    print "Define name for actor ", count, ":"
    name = raw_input ()
    nams.append(name)

if nams[2]: #I am trying to say 'if nams[2] exists, do something depending on len(nams)
    if len(nams) > 3:
        do_something
    if len(nams) > 4
        do_something_else

if nams[3]: #etc.
python-2.7 python
12 Answers

It can be done simply using the following code:

if index < len(my_list):
    print(index, 'exists in the list')
else:
    print(index, "doesn't exist in the list")
user_60399800

Oneliner:

do_X() if len(your_list) > your_index else do_something_else()

Full example:

In [10]: def do_X(): 
    ...:     print(1) 
    ...:                                                                                                                                                                                                                                      

In [11]: def do_something_else(): 
    ...:     print(2) 
    ...:                                                                                                                                                                                                                                      

In [12]: your_index = 2                                                                                                                                                                                                                       

In [13]: your_list = [1,2,3]                                                                                                                                                                                                                  

In [14]: do_X() if len(your_list) > your_index else do_something_else()                                                                                                                                                                      
1

Just for info. Imho, try ... except IndexError is better solution.

user_81876230

Here's a simple, if computationally inefficient way that I felt like solving this problem today:

Just create a list of available indices in my_list with:

indices = [index for index, _val in enumerate(my_list)]

Then you can test before each block of code:

if 1 in indices:
    "do something"
if 2 in indices:
    "do something more"

but anyone reading this should really just take the correct answer from: @user6039980

user_113434250
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