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Detailed Function Parameters
1. Default parameters
When calling the function, if the value of the default parameter is not passed in, the default value will be taken.
The following example will print the default age, if age is not passed in:
def printinfo(name, age=35):
# 打印任何传入的字符串
print("name: %s" % name)
print("age %d" % age)
# 调用printinfo函数
printinfo(name="miki") # 在函数执行过程中 age取默认值35
printinfo(age=9 ,name="miki")
The output of the above example:
name: miki
age: 35
name: miki
age: 9
Summary:
Parameters with values by default in formal parameters are called default parameters
Note: Parameters with default values must be at the end of the parameter list
def printinfo(name, age=35, sex):
print name
File "<stdin>", line 1
SyntaxError: non-default argument follows default argument
2. Indefinite length parameter
Sometimes it may be necessary for a function to handle more parameters than originally declared. These parameters are called variable-length parameters and will not be named when declared.
The basic syntax is as follows:
def functionname([formal_args,] *args, **kwargs):
"""函数_文档字符串"""
function_suite
return [expression]
Notice:
- The variable args with an asterisk (*) will store all unnamed variable parameters, args is a tuple
- The variable kwargs added with ** will store named parameters, that is, parameters in the form of key=value, and kwargs is a dictionary.
def test(a, b, *args, **kwargs):
"函数在声明时，需要两个参数"
print('a={},b={},args={},kwargs={}'.format(a,b,args,kwargs))
test(2, 3, '你好', 'hi', 'how do you do', name="zhangsan", age=18)
# a=2,b=3,args=('你好', 'hi', 'how do you do'),kwargs={'name': 'zhangsan', 'age': 18}
b = ('hi', '大家好', '今天天气真好')
d = {
'name': "zhangsan", "age": 19}
# 注意，在传入参数时的星号问题。
test(10, 20, *b, **d)
# a=10,b=20,args=('hi', '大家好', '今天天气真好'),kwargs={'name': 'zhangsan', 'age': 19}
# 如果在传值时，不使用星号，会把后面的参数当做 args
test(10,20,b,d)
# a=10,b=20,args=(('hi', '大家好', '今天天气真好'), {'name': 'zhangsan', 'age': 19}),kwargs={}
3. The default parameters are behind *args
def sum_nums_3(a, *args, b=22, c=33, **kwargs):
print(a)
print(b)
print(c)
print(args)
print(kwargs)
sum_nums_3(100, 200, 300, 400, 500, 600, 700, b=1, c=2, mm=800, nn=900)
Note:
If many values are variable-length parameters, then in this case, the default parameters can be placed after args, but if there are **kwargs, kwargs must be the last
mutable and immutable types
Summarize
-
The so-called variable type and immutable type refer to: data can be directly modified, if it can be directly modified, it is variable, otherwise it is immutable
-
Variable types (modify data, memory address will not change) are: list, dictionary, collection
-
Immutable types (modify data, memory address must change) are: numbers, strings, tuples
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