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Assume that obj already has a value of 42 when the code below starts running. Which of the subsequent statements reassign the variable? Which statements mutate the value of the object that obj references? Which statements do neither? If necessary, you can read the documentation.
obj = 'ABcd'
obj.upper()
obj = obj.lower()
print(len(obj))
obj = list(obj)
obj.pop()
obj[2] = 'X'
obj.sort()
set(obj)
obj = tuple(obj)
The comments in the following code show whether reassignment, mutation, or neither took place on each line of code:
obj = 'ABcd' # Reassignment
obj.upper() # Neither
obj = obj.lower() # Reassignment
print(len(obj)) # Neither
obj = list(obj) # Reassignment
obj.pop() # Mutation
obj[2] = 'X' # Mutation
obj.sort() # Mutation
set(obj) # Neither
obj = tuple(obj) # Reassignment
A simple assignment like var = something is always either an initialization or a reassignment. Since obj has already been initialized (it has a value of 42 before this code was reached), lines 1, 3, 5, and 10 perform reassignment. In a few situations, mutation and reassignment can happen in the same statement. None of the above statements do both.
obj.upper does not mutate the caller, so line 2 does neither. Likewise, since print, len, and set don't mutate their arguments, lines 4 and 9 are neither.
The remaining statements all mutate the object referenced by obj. pop removes the last element of the list. obj[2] = 'X' reassigns the element at index 2, but it mutates obj itself. Finally, sort mutates the object when it performs an in-place sort.
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