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
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 ...
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 ...
▶ 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_...
> Beware of default mutable arguments!/当心默认的可变参数! > Catching the Exceptions/捕获异常 > Same operands, different story!/同人不同命! > The out of scope variable/外部作用域变量 > Be careful with chained operations/小心链式操作 > Name resolution ignoring class scope/忽略类作用域的名称解析...
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!
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 ...
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 ...
Default parameters allow some arguments to be omitted when the function is called.Mutable Default Parameter ValuesThings can get weird if you specify a default parameter value that is a mutable object. Consider this Python function definition:Python...