Basic function exercises

Function basis

One 、 Call function

1. Call function
‘’’
Function name （ Argument list ）

1. Defining a function does not execute the function body , Call the function to execute the function body .（ How many calls , How many times will the function body be executed ）
2. When you call a function , The number of arguments is determined by the formal parameters of the called function .（ The process of assigning values to formal parameters with actual parameters is called parameter passing ）
3. Function call procedure （ Simple version ）
   When the code executes the function call statement , The subsequent execution process is as follows ：
   First step ： Return to the position defined by the function
   The second step ： The ginseng （ Assign values to formal parameters with arguments ）
   The third step ： Execute function body
   Step four ： Determine the return value （ For the time being ）
   Step five ： Returns the location of the function call , Then go back
   ‘’’

def func2(x, y, z):
    # x=10, y=20, z=30
    print(f'x:{
      x}, y:{
      y}, z:{
      z}')

Two 、 The parameters of the function

1. Location parameters and keyword parameters
   ‘’’
   According to the different ways of providing arguments when calling functions , Actual parameters are divided into position parameters and keyword parameters

1. Positional arguments
   Directly provide the data corresponding to the arguments , Let the arguments and formal parameters correspond in position one by one

2. keyword
   With ’ Shape parameter 1= Actual parameters 1, Shape parameter 2= Actual parameters 2, …' In the form of biography

3. A mixture of
   Positional parameters and keyword parameters can be used together , When used together, you must ensure that the location parameter is in front of the keyword parameter
   ‘’’

def func1(a, b, c):
    print(f'a:{
      a}, b:{
      b}, c:{
      c}')


#  Positional arguments 
func1(100, 200, 300)    # a:100, b:200, c:300
func1(200, 100, 300)    # a:200, b:100, c:300

#  Key parameters 
func1(a=100, b=200, c=300)     # a:100, b:200, c:300
func1(c=300, a=100, b=200)     # a:100, b:200, c:300

#  A mixture of 
func1(10, b=20, c=30)       # a:10, b=20, c=30
func1(10, c=20, b=30)       # a:10, b:30, c:20
func1(10, 20, c=30)         # a:10, b:20, c:30

2. Parameter default
‘’’
When defining a function, you can use ’ The name of the parameter = value ’ Provide default values for formal parameters in the form of ;
If a parameter has a default value , Then parameters with default values can be called without passing parameters .
If some parameters have default values when defining a function , Some parameters do not , Then the parameter without default value must be in front of the parameter with default value .
‘’’

def func2(a=10, b=20, c=30):
    print(f'a:{
      a}, b:{
      b}, c:{
      c}')


func2()                 # a:10, b:20, c:30
func2(100)              # a:100, b:20, c:30
func2(100, 200)         # a:100, b:200, c:30
func2(100, 200, 300)    # a:100, b:200, c:300
func2(c=300)            # a:10, b:20, c:300 ( Skip parameters with default values before , Pass the following parameters with keyword parameters )

def func3(a, c, b=20):
    print(f'a:{
      a}, b:{
      b}, c:{
      c}')


func3(20, 30)
func3(10, 20, 30)

3. Parameter type description
   ‘’’
   Parameters with default values ; What is the default value , Type description is what type
   Parameters without default ： You need to add ’: Type name ’
   ‘’’

def func4(x: list, y=''):
    pass

4. Indefinite length parameter
‘’’

1. belt Indefinite length parameter of – If you add , Then this formal parameter can accept any number of arguments
   belt * The essence of the indefinite length parameter of is a tuple , The corresponding multiple arguments are elements in tuples .

Be careful ：a. belt Indefinite length parameter of , Position parameters must be used when transferring parameters
b. If the fixed length parameter is in band After the parameter of （ Sometimes it's directly in * Behind ）, Then the following variable length parameter calls must use keyword parameters to pass parameters

2. belt ** Indefinite length parameter of ( understand )
   ‘’’

def func5(*x):
    pass


func5()
func5(10)
func5(10, 20)
func5(10, 20, 90, 8)

#  practice : Define a function to sum multiple numbers .
def sum2(*nums):
    s = 0
    for x in nums:
        s += x
    print(s)


sum2(10, 20)
sum2(10, 20, 30)

def func6(a, b, *c):
    print(f'a:{
      a}, b:{
      b}, c:{
      c}')


func6(10, 20)
func6(10, 20, 43, 56, 78, 90)


def func7(*a, b, c):
    print(f'a:{
      a}, b:{
      b}, c:{
      c}')


func7(10, 20, 30, 40, b=2, c=1)


def func8(*, a, b, c):
    print(f'a:{
      a}, b:{
      b}, c:{
      c}')


func8(a=10, b=20, c=30)


def func9(**x):
    print(x)


func9()
func9(a=10)
func9(a=10, b=20)
func9(a=10, b=20, x=100, y=200)


def func10(*args, **kwargs):
    pass


func10()
func10(10, 20, 30, 40)
func10(a=10, x=20, b=9)
func10(10, 20, x=2, y=9)

3、 ... and 、 The return value of the function

1. The function of return value is
   The function of return value is to convert the data generated inside the function , Pass to the outside of the function
   How do beginners determine whether a function needs a return value ： See if the function generates new data , If any, return the new data as the return value

2. Determine the return value of the function （ How to take data as return value ）
   ‘’’
   In the body of a function by return Keyword returns the return value of the function ：return data

Be careful ：1) If you do not encounter return, The return value of the function is None
2) return It also has the function of ending the function in advance （ Where to meet when executing the function body return, Where does the function end ）
‘’’

3. How to get the return value of a function outside of a function
   ‘’’
   To get the value of the function call expression is to get the return value of the function .
   Function call expression – The statement that calls the function
   Every function call statement actually has a result （ It's all data ）, This result is the return value of the function at the time of this call

The return value of a function depends on the time when the function is called return What is the following value ,return What is the following value , What is the result of the function call expression outside the function .
‘’’

def sum2(num1, num2):
    s = num1 + num2
    return s


a = sum2(78, 90)
print('a:', a)      # 168

print('========================================')

#  I haven't met return  The return value is None
def func3():
    print('abc')

result = func3()
print(' Return value :', result)   #  Return value : None


def func4(x):
    if x % 2:
        return 100


print(' Return value :', func4(20))    #  Return value : None
print(' Return value :', func4(21))    #  Return value : 100


def func5():
    for x in range(100):
        return x

print(func5())      # 0

Function job

1. Write a function , Exchange the specified dictionary key and value.

      for example :dict1={
         'a':1, 'b':2, 'c':3}  -->  dict1={
         1:'a', 2:'b', 3:'c'}  
   

   def func1():
       dict1 = {
         'a': 1, 'b': 2, 'c': 3}
       new_dict1 = {
         dict1[key]: key for key in dict1}
       return new_dict1
   
   
   print(func1())
   

2. Write a function , Extract all letters in the specified string , Then spliced together to produce a new string

       for example :  Pass in '12a&bc12d-+'   -->  'abcd'  
   

   def str3():
       str1 = '12a&bc12d-+'
       str2 = ''
       for x in str1:
           if 'a' <= x <= 'z' or 'A' <= x <= 'Z':
               str2 += x
       return str2
   
   
   print(str3())
   

3. Write your own capitalize function , Can change the first letter of the specified string into uppercase letter

      for example : 'abc' -> 'Abc'   '12asd'  --> '12asd'
   

   str1 = 'rjr43453'
   
   
   def str2():
       if 'a' <= str1[0] <= 'z':
           str3 = chr(ord(str1[0]) - 32) + str1[1:]
           return str3
       else:
           return str1
   
   
   print(str2())
   

4. Write your own endswith function , Determines whether a string has ended with the specified string

 for example :  character string 1:'abc231ab'  character string 2:'ab'  The result of the function is : True
      character string 1:'abc231ab'  character string 2:'ab1'  The result of the function is : False

def my_endswith(str1: str, str2: str):
    if len(str2) > len(str1):
        return False
    else:
        #  Reverse the string 
        str1 = ''.join(str1[::-1])
        str2 = ''.join(str2[::-1])
        #  Determine whether the short string is part of the beginning of the long string （ continuity ）
        for index1 in range(len(str2)):
            if str2[index1] != str1[index1]:
                return False
        return True


print(my_endswith('abc123', '123'))
print(my_endswith('abc321', '123'))

5. Write your own isdigit function , Determine whether a string is a pure numeric string

       for example : '1234921'   result : True
            '23 function '    result : False
            'a2390'     result : False
   

   def str2():
       str1 = '534uuuu55'
       for x in str1:
           if not '0' <= x <= '9':
               return False
       else:
           return True
       
       
   print(str2())
   

6. Write your own upper function , Change all lowercase letters in a string into uppercase letters

        for example : 'abH23 good rp1'    result : 'ABH23 good RP1'   
   

   def str2(str1):
       str3 = ''
       for x in str1:
           if 'a' <= x <= 'z':
               str3 += chr(ord(x)-32)
           else:
               str3 += x
       return str3
   print(str2('asd perform 13ATrh565'))
   

7. Write your own rjust function , Create a string whose length is the specified length , The original string is right justified in the new string , The rest is filled with the specified characters

       for example :  Original character :'abc'   Width : 7   character :'^'     result : '^^^^abc'         Original character :' how are you '   Width : 5   character :'0'     result : '00 how are you '
   

   def str1(x, y):
       a = x.rjust(7, '^')
       b = y.rjust(5, '0')
       return a, b
   
   
   print(str1('abc', 'wd'))
   

8. Write your own index function , Counts all subscripts of the specified elements in the specified list , If no element is specified in the list, return -1

       for example :  list : [1, 2, 45, 'abc', 1, ' Hello ', 1, 0]   Elements : 1    result : 0,4,6  
            list : [' zhaoyun ', ' Guo Jia ', ' Zhugeliang ', ' Cao Cao ', ' zhaoyun ', ' king of Wu in the Three Kingdoms Era ']   Elements : ' zhaoyun '    result : 0,4
            list : [' zhaoyun ', ' Guo Jia ', ' Zhugeliang ', ' Cao Cao ', ' zhaoyun ', ' king of Wu in the Three Kingdoms Era ']   Elements : ' Guan yu '    result : -1         
   

      def my_index(list1, item):
    new_list = []
    for i in range(len(list1)):
        if list1[i] == item:
            new_list.append(str(i))
    if new_list != []:
        return new_list
    else:
        return -1
   
   
    print(my_index([' zhaoyun ', ' Guo Jia ', ' Zhugeliang ', ' Cao Cao ', ' zhaoyun ', ' king of Wu in the Three Kingdoms Era '], ' zhaoyun '))
   

9. Write your own len function , Count the number of elements in the specified sequence

        for example :  Sequence :[1, 3, 5, 6]     result : 4
             Sequence :(1, 34, 'a', 45, 'bbb')   result : 5  
             Sequence :'hello w'     result : 7
   
   

def my_len(list1):
count = 0
for _ in list1:
count += 1
return count

print(my_len([1, 2, 3, 6, ‘ Love ’, ’ ', ‘ hate ’]))
```

10. Write your own max function , Gets the maximum value of the element in the specified sequence . If the sequence is a dictionary , Take the maximum value of the dictionary value

       for example :  Sequence :[-7, -12, -1, -9]     result : -1   
            Sequence :'abcdpzasdz'     result : 'z'  
            Sequence :{
          ' Xiao Ming ':90, ' Zhang San ': 76, ' Monkey D Luffy ':30, ' floret ': 98}    result : 98
    

    def my_max(nums):
    if type(nums) == dict:
       list_keys = [key for key in nums]
       max1 = nums[list_keys[0]]
       for x in range(1, len(list_keys)):
           if nums[list_keys[x]] > max1:
               max1 = nums[list_keys[x]]
       return max1
    else:
       max1 = nums[0]
       for y in range(1, len(nums)):
           if nums[y] > max1:
               max1 = nums[y]
       return max1
    
    
    print(my_max({
          ' Xiao Ming ': 90, ' Zhang San ': 76, ' Monkey D Luffy ': 30, ' floret ': 98}))
    print(my_max('abcdpzasdz'))
    print(my_max([-7, -12, -1, 9]))
    

11. Write a function to realize yourself in operation , Determine the number of... In the specified sequence , Whether the specified element exists

       for example :  Sequence : **(12, 90, 'abc')**    Elements : '90'      result : False
            Sequence : [12, 90, 'abc']    Elements : 90      result : True     
    

    def my_in(nums, item):
      for x in nums:
      	if item == x:
          	return True
      else:
      	return False
    
    
    print(my_in((12, 90, 'abc'), 'abc'))
    

12. Write your own replace function , Converts the old string specified in the specified string to the new string specified
    for example : Original string : ‘how are you? and you?’ Old string : ‘you’ New string :‘me’ result : ‘how are me? and me?’

def my_replace(str1, str2, str3):
    return str3.join(str1.split(str2))


print(my_replace('how are you? and you?', 'you', 'me'))