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The output of the code is:
B):
[1]
[1, 2]
“`python
def foo(x, lst=[]): # Defines a function ‘foo’ with parameters ‘x’ and ‘lst’. ‘lst’ has a default value of an empty list.
lst.append(x) # Appends the value of ‘x’ to the list ‘lst’.
return lst # Returns the modified list.
print(foo(1)) # Calls ‘foo’ with ‘x’ as 1. Since ‘lst’ is not provided, it uses the default empty list.
print(foo(2)) # Calls ‘foo’ again with ‘x’ as 2. The same list ‘lst’ is used, not a new empty list.
“`
When you run this code, you might expect to see two separate lists: `[1]` and `[2]`. However, the output will be:
“`
[1]
[1, 2]
“`
This happens because the default value for the `lst` parameter is evaluated only once when the function is defined, not each time the function is called. Therefore, the same list (`lst`) is used in subsequent calls to `foo` if the `lst` parameter is not provided.
To avoid this, you can use a default value of `None` and then create a new list inside the function if `lst` is `None`:
python
def foo(x, lst=None):
if lst is None:
lst = []
lst.append(x)
return lst
Now, each call to `foo` without a specific `lst` argument will result in a new list being created, and the output will be as initially expected:
[1]
[2]
This is a safer way to use mutable types as default arguments in Python functions.
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