Clever Geek Handbook

How can I check if a tuple exists in a Python list?

I am new to Python and I am trying to check if a pair exists [a,b]

in the list l=[[a,b],[c,d],[d,e]]

. I searched a lot of questions but couldn't find the exact solution. Please can someone tell me the correct and shortest way to do this?

when i run:

a=[['1','2'],['1','3']]
for i in range(3):
    for j in range(3):
        if [i,j] in a:
            print a

OUTPUT BLOCKED.

how to do it?

+3


source to share


5 answers


The code doesn't work because, '1' != 1

and therefore, ['1','2'] != [1,2]

If you want it to work, try:

a=[['1','2'],['1','3']]
for i in range(3):
    for j in range(3):
        if [str(i), str(j)] in a: # Note str
            print a


(But using in

or sets, as mentioned, is better)

+3


source


Here's an example:

>>> [3, 4] in [[2, 1], [3, 4]]
True


If you need to do this many times, consider using it because it has a much faster containment check. set

+11


source


In my interpreter (IPython 0.10, Python 2.7.2+), your code gives the correct output:

In [4]: a=[[1,2],[1,3]]

In [5]: for i in range(3):
   ...:         for j in range(3):
   ...:             if [i,j] in a:
   ...:                 print a
   ...: 
[[1, 2], [1, 3]]

(This should be a comment, but I cannot leave them.)

EDIT:

It turns out you had strings in the list a

. Then you need to convert yours int

to str

:

a=[['1','2'],['1','3']]
for i in range(3):
    for j in range(3):
        if [str(i), str(j)] in a:
            print a
0


source


This code works great for me:

>>> a = [[1, 2], [3, 4], [13, 11]]
>>> 
>>> for i in range(10):
...         for j in range(10):
...                 if [i, j] in a: 
...                         print [i, j] 
... 
[1, 2]
[3, 4]
>>>

I'm not sure what is wrong with your code. You probably don't have "]" in the first line.

0


source


Don't forget that [a, b] is not [b, a] in python, so you can order 2 values ​​in your tuples if you want to consider [A, B] and [B, A] the same thing:

You can also use set (your_list) if your list is large and redundant.

In the example code, you are compiling integers and strings:

['1', '2'] # this is a 2-list of strings '1' and '2'
[1, 2] # this is a 2-list of integers 1 and 2
0


source






More articles:


All Articles