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Python Lists, Tuples and Slicing, what does print(b) print after a = [3, 1, 2]?
Block 4, Lists, Tuples and Slicing, question 2 of the Python sample
a = [3, 1, 2]
b = a.sort()
print(b)What does this print?
Show the answer and why each option is right or wrong
Answer, A. None
- A. None
- Correct. list.sort() sorts the list in place and returns None, so b ends up holding None regardless of how a itself changed.
- B. [1, 2, 3]
- Assumes sort() returns the sorted list, the way sorted() does, instead of mutating in place and returning nothing.
- C. [3, 1, 2]
- Assumes sort() returns a reference to the list before it was sorted.
- D. True
- Assumes an in place mutating method reports success as a boolean rather than returning None.
Methods that mutate a list in place, such as sort, reverse, append and extend, consistently return None so that their result is never mistaken for a new object. To get the sorted list itself, the value has to be read from the variable that was sorted, not from the method call.
The answer above is what the CPython interpreter printed when the snippet was run, not what someone expected it to do.
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