Just as you wrote it:

>>> matrix = [["str1", "str2"], ["str3"], ["str4", "str5"]]
>>> matrix
[['str1', 'str2'], ['str3'], ['str4', 'str5']]
>>> matrix[0][1]
'str2'
>>> matrix[0][1] += "someText"
>>> matrix
[['str1', 'str2someText'], ['str3'], ['str4', 'str5']]
>>> matrix[0].extend(["str6"])
>>> matrix[0]
['str1', 'str2someText', 'str6']

Just think about 2D matrix as list of the lists. Other operations also work fine, for example,

>>> matrix[0].append('value')
>>> matrix[0]
[0, 0, 0, 0, 0, 'value']
>>> matrix[0].pop()
'value'
>>> 

No, it shows everything there is, to remove it, you need to do some string replacing stuff:

print(str(shape).replace("'", '').replace('], [', '],\n ['))

Which outputs:

[[, , ],
 [, , ],
 [, , ]]

Like so:

[ item for innerlist in outerlist for item in innerlist ]

Turning that directly into a string with separators:

','.join(str(item) for innerlist in outerlist for item in innerlist)

Yes, the order of 'for innerlist in outerlist' and 'for item in innerlist' is correct. Even though the "body" of the loop is at the start of the listcomp, the order of nested loops (and 'if' clauses) is still the same as when you would write the loop out:

for innerlist in outerlist:
    for item in innerlist:
        ...

Use ast.literal_eval

>>> list_string = '[[1, 1], [2, 2], [3, 3]]'
>>> import ast
>>> type(ast.literal_eval(list_string))
<type 'list'>

Python 3.x

print ( [list( map(int,i) ) for i in l] )

Output :

[[1, 1, 3], [2, 3, 5], [3], [4, 5], [5, 1], [6, 6], [7]]

You can assign the 2D list (list is the term for an array used in Python):

data = [["a", "b", "c", "d"], ["e", "f", "g", "h"]]

Next you can loop through each list inside the data list and assign the new value to the original value in the list:

idx = 0
for x in data:
    data[idx] = "".join(x)
    idx += 1

This will return the required output.

Full Code:

data = [["a", "b", "c", "d"], ["e", "f", "g", "h"]]
idx = 0
for x in data:
    data[idx] = "".join(x)
    idx += 1

Test your code by adding the following two lines:

print(f'First value in list: {data[0]} and second value in list: {data[1]}')

Explanation:

data = [["a", "b", "c", "d"], ["e", "f", "g", "h"]]

The line of code above assigns the 2D list to a variable to be used on later.

idx = 0

The variable idx is used to assign the required value to each of the former values of the 2D list data. You can also assign each value to a separate list by using the .append method.

for x in data:

This loops through each value (or list) inside of the list data, using the variable x to be referenced as in the code. This can also be done using a while loop.

data[idx] = "".join(x)

This assigns the former value with the index of idx in the list with the new value. This uses the python .join method to connect the values in the list by a "".

To read more about the Python .join method visit:

https://www.w3schools.com/python/ref_string_join.asp

idx += 1

This is used to add 1 to the former value of idx so that it outputs the new index of the next value in the list used in the for loop.

Testing Your Code

print(f'First value in list: {data[0]} and second value in list: {data[1]}')

the above line of code is a simple formatted string that outputs the first data[0] and second data[1] values of the variable data.

I hope this helps you with your coding and understanding your code.

[sentence.split(' ')  for sentence in sentences]