SoFunction
Updated on 2024-11-20

Python functions and python anonymous functions lambda in detail

1. python functions

1.1 Role of functions

  • The function iswell organizedThe.Reusableof code segments used to implement a single or associated functionality
  • Functions can raiseHighly applied modularitycap (a poem)Reuse of code
  • python built-in functions:/zh-cn/3.10/library/

1.2 Function definitions

  • def: function definition keywords
  • function_name: Function name
  • (): where the parameter list is placed, can be empty
  • parameter_list: Optional, specify the parameters to be passed to the function.
  • comments: Optional, specify comments for the function
  • function_body: Optional, specify the function body
def function_name([parameter_list]):
    [''' comments ''']
    [function_body]

Notes on defining functions:

  • Indentation: python judges blocks of code by strict indentation.

    • Function bodies and comments must be indented relative to the def keyword, usually by 4 spaces.
    • pycharm auto-formatting shortcuts:ctrl+alt+L

  • Defining empty functions

    • utilizationpass statement placeholder
    • Write function comment comments,

1.3 Function calls

  • function_name: name of the function
  • parameter_value: optional, specify the value of each parameter.
function_name([parameter_value])

1.4 Parameters of functions

1.4.1 Passing of parameters

  • Formal parameters:Defining FunctionsThe parameter in parentheses after the name of the function is used when
  • Actual parameters:call functionThe parameter in parentheses after the name of the function is used when
# a, b, c are formal parameters
def demo_func(a, b, c):
    print(a, b, c)

# 1, 2, 3 are actual parameters
demo_func(1, 2, 3)

1.4.2 Parameter types

1.4.2.1 Positional parameters (required parameters)

  • Quantity must be the same as when defined
  • The position must be the same as when defined
def demo_func(a, b, c):
    print(a, b, c)

# 1 to a, 2 to b, 3 to c #
demo_func(1, 2, 3)

1.4.2.2 Keyword parameters

  • utilizationThe name of the formal parameter determines the value of the input parameter
  • Doesn't need to be exactly the same position as the formal parameter
def demo_func(a, b, c):
    print(a, b, c)

demo_func(a=1, b=2, c=3)

1.4.2.3 Variable parameters

  • Variable parameters are also known asindeterminate length parameter (math.)
  • The actual parameters in the incoming function can be any number of them
  • common form
    • *args
    • **kwargs
1.4.2.3.1 *args
  • Receive anyMultiple actual parametersand put it into atuplecenter
  • Use the already existinglistingsmaybetupleAs a variable argument to a function, the name of the list can be preceded by the* 
def print_language(*args):
    print(args)

print_language("python", "java", "php", "go")

params = ["python", "java", "php", "go"]
print_language(*params)
1.4.2.3.2 **kwargs
  • Receive any number ofActual parameters that are explicitly assigned like keyword parametersand put it into adictionariescenter
  • Using an already existing dictionary as a variable argument to a functionYou can prefix the name of the dictionary with** 
def print_info(**kwargs):
    print(kwargs)

print_info(Tom=18, Jim=20, Lily=12)

params = {'Tom':18, 'Jim':20, 'Lily':12}
print_language(**params)

1.4.5 Setting default values for parameters

  • When defining a function you canSpecify default values for formal parameters
  • The formal parameter that specifies the default value must be placed at the end of all parameters.Otherwise, a syntax error will be generated
  • param=default_value: Optional, specifies the parameter and sets the default value for the parameter to default_value.
  • Setting default valuesUnavailable objects must be used, mutable objects are not available, e.g., lists, dictionaries.
def function_name(..., [param=default_value]):
    [function_body]

1.5 Function Return Values

value: optional, specify the value to be returned

def function_name([parameter_list]):
    [''' comments ''']
    [function_body]
    return [value]

2. python lambda expressions

2.1 Anonymous functions

  • Functions without names
  • Creating Anonymous Functions with Lambda Expressions

2.2 Scenarios of use

  • Need a function, but don't want to bother naming the function
  • Usually in thisScenarios where the function is only used once
  • You can specify short callback functions

2.3 Grammar

  • result: calls a lambda expression.
  • [arg1 [, arg2, .... , argn]]: optional, specifies the list of parameters to pass
  • expression: mandatory, specify an expression that realizes a specific function.
result = lambda [arg1 [, arg2, .... , argn]]: expression

2.4 Examples

L=[('b',2),('a',1),('c',3),('d',4)]

# 2, using the parameter cmp sort
sorted(L, cmp=lambda x,y:cmp(x[1],y[1]))
# Results:
[('a', 1), ('b', 2), ('c', 3), ('d', 4)]
# 3, using the parameter key sort
sorted(L, key=lambda x:x[1])
# Results:
[('a', 1), ('b', 2), ('c', 3), ('d', 4)]

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