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number = 1 + 2 |
# Output the value of number to confirm it is set to 3 |
print(number) |
# Create another variable called 'other' and assign it the value of 'number' |
other = number |
# Output the value of other to confirm it is also set to 3 |
print(other) |
# It might be tempting to think that the values are "stored into" the variable, |
# and this terminology is used casually. But in Python all variables are really |
# labels, or more accurately, references to a value stored in memory. So in the |
# above example, both number and other reference the same value '3' in memory. |
# If we only work with numeric type values this distinction may not matter, but |
# if we work with things like lists or objects this distinction can become |
# very important. |
# list1 will refer to a list in memory with elements 1,2,3 |
list1 = [1,2,3] |
# This will NOT create a copy of the list in memory... this will set list2 to |
# refer to the SAME list in memory that list1 refers to. So if we then |
# modify list2[0] below, it will modify the SAME list in memory that list1 |
# refers to... we'll see this as both list1 and list2 will be output as the |
# same modified list. |
# |
list2 = list1 |
# We could actually create a copy of the list in memory with list1.copy(), this |
# create a duplicate list that list2 will now refer to. THEN if we were to |
# modify list2 it would not effect the list that list1 is referring to as they |
# now each refer to separate lists. It's important that we understand that |
# using variables and the assignment operator does NOT create a copy, if we |
# write our code with this understanding we may introduce logic bugs into our |
# program when things are unexpectedly modified. |
# |
# list2 = list1.copy() |
# If we modify list2, it will modify the same list that list1 refers to as list2 |
# refers to this list also! |
# |
list2[0] = 10 |
# When we output list1 and list2, we'll get the same (now modified) list with |
# the first element set to '10'. We might think that list2 = list1 would create |
# a copy of "list1" and store it into list2, but this is not what the assignment |
# operator does. |
# |
print("list1:", list1) |
print("list2:", list2) |
# We can assign the same value to multiple variables like this, where both q and |
# w will be set to '100'. |
q = w = 100 |
# Output q and w to confirm they are both set to 100 |
print("q:", q, "w:", w) |
# We can assign multiple different values to multiple variables with this |
# assignment operation... |
q, w = 2, 8 |
# Output q and w to confirm that q is 2 and w is 8 |
print("q:", q, "w:", w) |
# We can use this technique to swap the values stored in variables, here we swap |
# the values of q and w. |
q, w = w, q |
# Output q and w to confirm the swap, that q is now 8 and w is now 2 |
print("q:", q, "w:", w) |
# The 7 arithemtic operators: |
# |
# + addition |
# - substraction |
# * multiplication |
# ** power |
# / division |
# // floor division |
# % modulus |
# |
# Each have an assignment operator version which combines assignment with the |
# arithmetic operation. |
# |
# Set number to 1 |
number = 1 |
# We could add 2 to number like this... but then we would have to repeat the |
# variable name 'number' |
# |
# number = number + 2 |
# Or we could use the += operator which adds 2 to the value of number and stores |
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