Question:

I am new to Python, and I am trying to check whether a pair `[a,b]`

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

. I searched many questions, but couldn't find precise solution. Please can someone tell me the right and shortest way of doing it?

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 IS BLANK

how to achieve this then?

Answer1:The code does not work because `'1' != 1`

and, consequently, `['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 already mentioned is better)

Here is an example:

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

If you need to do this a lot of times consider using a <strong>`set`

</strong> though, because it has a much faster containment check.

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]]
```

<em>(This should be a comment, but I can't leave them yet.)</em>

EDIT:

Turns out you had strings in the `a`

list.
Then you need to convert your `int`

s to `str`

as well:

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

Answer4:This code works fine 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. For sure you have missing ']' in first line.

Answer5:Don't forget that [a, b] is not [b, a] in python so you might want to order the 2 values in your tuples if you want to consider [A, B] and [B, A] is the same:

You might also want to use set(your_list) if your list is big and it has redundancy.

In your code example you are compaing 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
```