Python: square brackets

Question

I'm comparing two chunks of code:
aaa = ["abcdef"]
bbb = ["ghijklmnop"]
print (aaa[0][0:4]+bbb[0][3:7]) ### outputs abcdjklm
aaa = ["abcdef"]
bbb = ["ghijklmnop"]
print (aaa[0:4]+bbb[3:7]) ### outputs ['abcdef']
Why does the second chunk of code not include letters from list bbb?
What do the first sets of square brackets tell us?
ie. aaa[ ] [ ] + bbb[ ][ ]
^ ^
^ ^
^ ^

Answer 1

Those first square brackets tells us the first element in list
aaa[0:4] means slice elements in list from index 0 upto index4-1 and return them but aaa only includes one element i.e. "abcdef"
Second square bracket will slice from the string

Answer 2

a[0][0:4] means list a's 0th value which is "ab def" now for this slicing [0:4] return 0 to 3 charecters from it those are "abcd"
Similarly b[0][3:7] return jklm
In 2nd code a[0:4] means slice list values from 0 to index 3 but you have value at index 0 only, other returns empty so total value at index 0 returned and similarly b has also value at index 0 only , so slicing 3:7 to returns empty list..
So finally it only "a cdef"
[0] is value at index position 0, [0:4] is slicing values from 0 index to 3. (4-1).