1、The Hitchhiker’s Guide to Python Python’s default arguments are evaluatedoncewhen the function is defined, not each time the function is called (like it is in say, Ruby). This means that if you use a mutabl
Mutable default parameter If python function default input is mutable, calling the function will change on top of. defmutable_parameter(lst=[]):iflstisNone:lst=[]lst.append(1)returnlstprint(mutable_parameter())print(mutable_parameter())[1][1]use'lst=None'instead! Modifying while iterating F...
not each time the function is called (like it is in say, Ruby). This means that if you use a mutable default argument and mutate it, you will and have mutated that object for all future calls to the function as well.
Default arguments are a helpful feature, but there is one situation where they can be surprisingly unhelpful. Using a mutable type (like a list or dictionary) as a default argument and then modifying that argument can lead to strange results. It's usually best to avoid using mutable default ...
Passing mutable lists or dictionaries as default arguments to a function can have unforeseen consequences. Usually when a programmer uses a list or dictionary as the default argument to a function, the programmer wants the program to create a new list or dictionary every time that the function ...
A common practice to avoid bugs due to mutable arguments is to assign None as the default value and later check if any value is passed to the function corresponding to that argument. Example: def some_func(default_arg=None): if default_arg is None: default_arg = [] default_arg.append(...
This basically means that the default argument of the function is changing every time we run it. When we run the script, Python evaluates the function definition only once and creates the default list and the default value. Because lists are mutable, every time you call the function you will...
4. def foo(x, alist=[ ])可变数据类型(mutable)作为默认参数导致的问题。 def foo(x, alist=[ ])中,默认参数alist=[ ]只有定义函数的时候被评估。所以在调用时,alist依旧是定义函数时的同一个列表,即使我们重写调用函数alist不会被清空。 # 定一个fruit函数 def fruit(x, alist = []): """添加...
Mutable Default Parameter Values Pass-By-Value vs Pass-By-Reference in Pascal Pass-By-Value vs Pass-By-Reference in Python Argument Passing Summary Side Effects The return Statement Exiting a Function Returning Data to the Caller Revisiting Side Effects Variable-Length Argument Lists Argument Tuple ...
Python allows you to specify that a function argument is optional by providing a default value for it. While this is a great feature of the language, it can lead to some confusion when the default value is mutable. For example, consider this Python function definition: >>> def foo(bar=[...