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Detailed explanation of function parameter passing in python

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Jul 22, 2016 am 08:56 AM

python Function parameters Function parameter passing Function parameter type

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

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The functions defined above are used as follows:

Pass in multiple parameters,

calc(1, 2, 3, 4)
30 #函数返回值

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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

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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'}

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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'}

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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'
>>>

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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'
>>>

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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)

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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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