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Detailed explanation of function parameter passing in python
Detailed explanation of function parameter passing in python
1. Parameter input rules
Variable parameters allow 0 or any number of parameters to be passed in, which will be automatically assembled into a tuple when the function is called;
Keyword parameters allow 0 or any number of parameters to be passed in, which will be automatically assembled into a dict when the function is called;
1. Pass in variable parameters:
def calc(*numbers):
sum = 0
for n in numbers:
sum = sum + n * n
return sum
The functions defined above are used as follows:
Pass in multiple parameters,
calc(1, 2, 3, 4) 30 #函数返回值
Pass in a list,
nums = [1, 2, 3] calc(*nums) # 通过 * 将list中的元素作为可变参数传入函数 14 # 函数返回值
2. Pass in keyword parameters:
>>> def person(name, age, **kw):
... print('name: ', name, 'age: ', age, 'other: ', kw)
...
>>>
>>> person('luhc', 24, city='Guangzhou')
name: luhc age: 24 other: {'city': 'Guangzhou'}
Similarly, a predefined dict can be passed into the above function as a parameter:
>>> info = {'city': 'Guangzhou', 'job': 'engineer'}
>>>
>>> person('luhc', 24, **info)
name: luhc age: 24 other: {'city': 'Guangzhou', 'job': 'engineer'}
Note: The function person obtains a copy of the parameter info. Modification within the function will not affect the value of info
3. In keyword parameters, you can limit the name of keyword parameters:
# 通过 * 分割，以指定关键字参数名
>>> def person(name, age, *, city, job):
... print('name: ', name, 'age: ', age, 'city: ', city, 'job: ', job)
...
>>>
>>> person('luhc', 24, city='Guangzhou', job='engineer')
name: luhc age: 24 city: Guangzhou job: engineer
# 如果传入参数中，存在参数名不在定义的范围内，将抛出异常
>>> person('luhc', 24, city='Guangzhou', jobs='engineer')
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: person() got an unexpected keyword argument 'jobs'
>>>
In addition, if variable parameters have been specified in the function, * can be omitted, as follows:
# 省略了用 * 作为分割，指定关键字参数名
>>> def person(name, age, *args, city, job):
... print('name: ', name, 'age: ', age, 'args: ', args, 'city: ', city, 'job: ', job)
...
>>>
>>> person('luhc', 24, 'a', 'b', city='Guangz', job='engineer')
name: luhc age: 24 args: ('a', 'b') city: Guangz job: engineer
>>>
# 同样，如果传入了关键字参数未指定的参数名，则抛出异常
>>> person('luhc', 24, 'a', 'b', city='Guangz', job='engineer', test='a')
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: person() got an unexpected keyword argument 'test'
>>>
2. Parameter combination use:
The order of parameter definition must be: required parameters, default parameters, variable parameters, named keyword parameters and keyword parameters
def f1(a, b, c=0, *args, **kw):
print('a =', a, 'b =', b, 'c =', c, 'args =', args, 'kw =', kw)
def f2(a, b, c=0, *, d, **kw):
print('a =', a, 'b =', b, 'c =', c, 'd =', d, 'kw =', kw)
The above is all the content introduced to you in this article. I hope it will be helpful to everyone in understanding the passing of function parameters in Python
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