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 mutable default argument and mutate it, youwilland have mutated that object for a...
下面我们来看看使用可变默认参数(Mutable default arguments)时会出现什么诡异的情况。 你可能写了以下函数,它有一个默认参数是一个list: defappend_to(element, to=[]): to.append(element)returnto 然后调用该函数: my_list = append_to(12)print(my_list) my_other_list= append_to(42)print(my_other_l...
...0, 1, 2] 140670243756736 [0, 1, 0, 1] 有没有发现,第一个 func(2) 和第二个 func(2) 的 id 是一样的,说明它们用到的是 li 是同一个,这就参数的默认值是可变对象的逻辑...如果要深入研究 Python 为什么这么设计,可以移步 http://cenalulu.github.io/python/default-mutable-arguments/...
下面我们看看使用可变默认参数(Mutable default arguments)时会出现什么莫名其妙的状况。 你可能写了以下函数,它有一个默认参数是一个list: def append_to(element, to=[]): to.append(element) return to 1. 2. 3. 然后调用该函数: my_list = append_to(12)print(my_list)my_other_list = append_to(4...
This makes a difference when the default is a mutable object such as a list, dictionary, or instances of most classes. For example, the following function accumulates the arguments passed to it on subsequent calls: 我们来看看解释分析下,Python官方文档给出的理由就是Python对默认值只计算...
Python’s default arguments are evaluated once when the function is defined, 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 ...
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 ...
▶ Beware of default mutable arguments!def some_func(default_arg=[]): default_arg.append("some_string") return default_argOutput:>>> some_func() ['some_string'] >>> some_func() ['some_string', 'some_string'] >>> some_func([]) ['some_string'] >>> some_func() ['some_...
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!
FBT002 boolean-default-value-in-function-definition FBT003 boolean-positional-value-in-function-call B002 unary-prefix-increment B003 assignment-to-os-environ B004 unreliable-callable-check B005 strip-with-multi-characters B006 mutable-argument-default ...