I am a little confused regarding the assignment statement inside the code block of a for loop.
EXAMPLE CODE:
my_list = ['1', '2', '3', '4']
my_new_list = []
for element in my_list:
element = int(element) ** 2
my_new_list.append(str(element))
print(my_new_list)
Basically, I'm having trouble understanding this assignment statement from the code above:
element = int(element) ** 2
I know that the expression on the right side of the = gets evaluated first and then it is assigned to the variable on the left side of the =. But I've learned that by using the for loop, the variable in loop header (here being element) gets assigned each value of the iterable (here being my_list) step by step.
So my mind basically sees these statements (which I know there are syntactically wrong, as you cannot assign a value to a string literal):
'1' = int('1') ** 2
'2' = int('2') ** 2
'3' = int('3') ** 2
'4' = int('4') ** 2
However, when I run the above code through Python Visualizer it shows me that everything is fine and that the variable element gets assigned the values 1, 4, 9 and 16 respectively.
How is this possible? Is there an exception for this in Python when using for loops?
There's nothing special about the loop. The first thing each iteration does is assign a value from my_list to the variable element. You then simply assign a new value to element, based on the old value. When the iteration completes, the loop again assigns another value from my_list to element.
Unrolling the loop
my_new_list = []
for element in my_list:
element = int(element) ** 2
my_new_list.append(str(element))
would give you something like
my_new_list = []
itr = iter(my_list)
element = next(itr) # '1'
element = int(element) ** 2
my_new_list.append(str(element))
element = next(itr) # '2'
element = int(element) ** 2
my_new_list.append(str(element))
element = next(itr) # '3'
# etc
You're never assigning "to" a str value; you're just replacing the str value previously held by element with an int value.