This is the code I'm trying to run:
def Menu():
##Menu actions
old=stock_list[:]
print(old+" before")
Save(stock_list[:])
print(old+" after")
def Save(list_of_stock):
##change each element of the list to be a code object
This is the output I get:
[["DVI cable"], [], [], []] before
[[<code object <module> at 0x037630F0, file "<string>", line 1>], [], [], []]
As you can see, even though in the 'Menu' function, old shouldn't change, but it does
when you pass old as an argument to Save a shallow copy of old is passed into Save. When you do some changes in Save it got reflected in old as well. using deepcopy to pass that list will prevent that from happening.
from copy import deepcopy
def Menu():
##Menu actions
old = stock_list[:]
print(f"{old} before")
Save(deepcopy(old))
print(f"{old} after")
copy.copy(x) Return a shallow copy of x.
copy.deepcopy(x) Return a deep copy of x.
The difference between shallow and deep copying is only relevant for compound objects (objects that contain other objects, like lists or class instances)
A shallow copy constructs a new compound object and then (to the extent possible) inserts references into it to the objects found in the original.
A deep copy constructs a new compound object and then, recursively,
inserts copies into it of the objects found in the original.
