print([[i+j for i in "abc"] for j in "def"])

Question

I'm new to Python.

I stumped upon with one of this comprehension

print([[i+j for i in "abc"] for j in "def"])

Could you please help me convert the comprehension in for loop?

I'm not getting the desired result by for loop:

list = []
list2 = []

for j in 'def':
    for i in 'abc':
        list.append(i+j)
    list2 = list
print (list)

the above is my try with for loop. I' missing something. Below should be the desired result in for loop that i want.

([[‘ad’, ‘bd’, ‘cd’], [‘ae’, ‘be’, ‘ce’], [‘af’, ‘bf’, ‘cf’]])

which I believe is a matrice.

Thanks in advance.

I tried your code and I got your result. Can you clarify the problem? — SurDin, Sep 07 '16 at 14:57
Recommended read http://stackoverflow.com/questions/34835951/what-does-list-comprehension-in-python-mean-how-does-it-work-and-how-can-i-us — Bhargav Rao, Sep 07 '16 at 14:57
there are 2 for loops in this code! the result is `[['ad', 'bd', 'cd'], ['ae', 'be', 'ce'], ['af', 'bf', 'cf']]`. what is your expected result? — Francesco Nazzaro, Sep 07 '16 at 14:57
If you are getting an *unexpected* result, that implies you have a for loop that you are using to get it. Please share your loop here. — chepner, Sep 07 '16 at 14:58
i want to use the above comprehension in terms of for loop. hre is what i tried with list = [] list2 = [] for j in 'def': for i in 'abc': list.append([i+j]) list2 = list print (list) — Sunil, Sep 07 '16 at 14:58
Code seems fine. It's not a matrix though, it's a list of lists. — RemcoGerlich, Sep 07 '16 at 14:59
Do not use `list` as a name for a variable. It silently trashes the function `list()` of the same name. — dawg, Sep 07 '16 at 15:26

score 4 · Answer 1 · answered Sep 07 '16 at 15:03

The easiest thing to unravel a comprehension like this is to take it one comprehension at a time and write that as a loop. So:

[[i+j for i in "abc"] for j in "def"]

becomes:

outer_list = []
for j in "def":
    outer_list.append([i + j for i in "abc"])

Alright, cool. Now we've gotten rid of the outer comprehension so we can unravel the inner comprehension next:

outer_list = []
for j in "def":
    inner_list = []
    for i in "abc":
        inner_list.append(i + j)
    outer_list.append(inner_list)

score 1 · Answer 2 · answered Sep 07 '16 at 15:00

1

For loop for this comprehension will look like this

result = []
for j in "def":
    r = []
    for i in "abc":
        r.append(i+j)
    result.append(r)

answered Sep 07 '16 at 15:00

score 1 · Answer 3 · answered Sep 07 '16 at 15:03

1

a = 'abc'
b = 'def'

>>> [[x+y for x in a]for y in b]
[['ad', 'bd', 'cd'], ['ae', 'be', 'ce'], ['af', 'bf', 'cf']]

Loop

>>> for y in b:
...     for x in a:
...         print x+y,
... 
ad bd cd ae be ce af bf cf

answered Sep 07 '16 at 15:03

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