Méthode d'utilisation et exemple de copy() de la liste Python

Python list methods

The copy() method returns a shallow copy of the list.

listcan be copied using=Operators. For example:

old_list = [1,　2,　3]
new_list = old_list

The problem with copying lists in this way is that if you modify new_list, old_list will also be modified.

old_list = [1,　2,　3]
new_list = old_list
# Add an element to the list
new_list.append('a')
print('New list:', new_list)
print('Old list:', old_list)

When running the program, the output is:

New list:　[1,　2,　3, 'a']
Old list:　[1,　2,　3, 'a']

However, if you need the original list to remain unchanged while modifying the new list, you can use the copy() method. This is called a shallow copy.

The syntax of the copy() method is:

new_list = list.copy()

copy() parameters

copy() has no parameters.

copy() return value

The copy() function returns a list. It does not modify the original list.

Example1：Copy list

# Mixed list
list = ['猫', 0,　6.7]
# Copy a list
new_list = list.copy()
# Add an element to the new list
new_list.append('狗')
# Print the new and old lists
print('Old list:　', list)
print('New list:　', new_list)

When running the program, the output is:

Old list:　['猫', 0,　6.7]
New list:　['猫', 0,　6.7, 'dog']

As you can see, even if the new list is modified, the old list remains unchanged.

You can also achieve the same result using slicing:

Example2：Shallow list copy using slicing

# Mixed list
list = ['cat', 0,　6.7]
# Copy a list using slicing
new_list = list[:]
# Add an element to the new list
new_list.append('dog')
# Print the new and old lists
print('Old list:　', list)
print('New list:　', new_list)

After running, the output result is:

Old list:　['cat', 0,　6.7]
New list:　['cat', 0,　6.7, 'dog']

Python list methods