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How to Pass List by Value as Parameter in Python
source link: https://jdhao.github.io/2022/07/27/pass_list_by_value_python/
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How to Pass List by Value as Parameter in Python
2022-07-27
171 words
1 min read
48 times read
If we pass list as parameter to a function and change the parameter, the original list is also changed. This is because list is a mutable type, when we pass list to a function, we are passing the same list.
def my_fun(my_list):
my_list.append(1)
return my_list
x = [1, 2, 3]
y = my_fun(x)
print(f"x: {x}, y: {y}")
# x, y are both [1, 2, 3, 1]
How can we pass the “value” of this list instead of its “reference”? We can use several ways:
- slicing:
my_fun(x[:]) - list():
my_fun(list(x)) list.copy():my_fun(x.copy())copy.copy():my_fun(copy.copy(x))copy.deepcopy():my_fun(copy.deepcopy(x))
The first four ways only create a shallow copy of the original list. They only work for simple list consisting of immutable types, for example, a list of int. If the list element is a mutable type themselves, they will not work.
Only the copy.deepcopy() method can truly create a new list.
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