Python Base Two

//fourth day to study python

24. In python , how to create funcation.

    we can use def to define funcation. such as:

    def MyFirstFuncation():

            print('this is my first funcation')

    MyFirstFuncation()

    -> this is my first funcatio.

    if there are no MyFirstFuncation , it will be have an error.

    of course , we can pass a parameter

    def MySecondFuncation(language):

            print(' i love  ' + language)

    MySecondFuncation('python')

    ->i love python

    if parameter is more , we can use comma divided parameter, such as:

    def AddFuncation(num1,num2):

              print(num1 + num2)

    -> 3

    how to use return:

    def SubFuncation(num1,num2):

              return (num1 - num2)

    print(SubFuncation(6,3))

    -> 3

    ok , next to study

    def myFuncation(m):

         'do you know what is funcation'

          #this is secret

          print('my'+m+'roy')

    myFuncation.__doc__

    -> do you know what is funcation

    next example:

    def sortFuncation(str1,str2):

            print(str1,str2)

    sortFuncation('second','first')

    -> second first

    sortFuncation(str2 = 'second', str1 = 'first')

    -> first second

    default funcation:

    def defaultFuncation(name='wyg',age='12'):

             print(my name is '+name+'age is '+age)

     defaultFuncation()

     -> my name is wyg age is 12

    def textPara(*paras):
           print('parameters length is:',len(paras))
           print('the second parameters is:',paras[1])

    textPara(1,2,3,'roy')
    ->

    parameters length is: 4
    the second parameters is: 2

    def textPara(*paras,exp):
           print('parameters length is:',len(paras),exp)
           print('the second parameters is:',paras[1])

    textPara(1,2,3,'roy',exp = 6)
    ->

    parameters length is: 4 6
    the second parameters is: 2

//fifth day to study python(2016/8/6)

25. In python ,how to return one or more value, such as:

    def back():

           return [1,3.14,'roy']

     print(back())

     -> [1,3.14,'roy']

 

    def back():

           return 1,3.14.'roy'

    print(back())

    -> (1,3.14,'roy')

 

26. In python , Local Variable and Global Variable . Look at example,

      def textFuncation(num1, num2):

              result = num1 * num2

              return result

       num1_input = float(input('input num1:'))

       num2_input = float(input('input num2:'))

       res = textFuncation(3,5)

       print(result is:',res)

       -> result is 15

       now we analyse which is local variable and which is global variable

       num1,num2,result is local variable

       num1_input,num2_input,res is global variable

       but we need to know if we modify global variable in funcation , global variable will not change , it will create a local variable  with the same name global name ,we can access global variable in funcation ,but try not to modify it. if you want  to mofify it , we continue to study it.

 

27.  In python , if you want to change global variable in funcation ,how to achieve it.

       count = 5

       def myFun():

             global count

             count = 10

             print(count)

        myFun()

        print(count)

        -> 10, 10

        if you not to use global ,the result is 10, 5

 

28. In python , how to invoke a funcation in another funcation, the follow is most simple example:

      def fun1():

            print('fun1 is using')

            def fun2():

                  print('fun2 is using')

            fun2()

      fun1()

      ->

      fun1 is using

      fun2 is using

      fun2 not invole by other except fun1

 

29. In python , support lambda, such as:

      def fun(x):

               return 2 * x + 1

      fun(5)

      -> 11 

      g = lambda x : 2 * x + 1

      g(5)

      -> 11

      g = lambda x, y : x + y

      g(3,4)

      -> 7

 

30. In python , there are two important built-in funcation i will introduce it

      first is filter(None or funcation, iterable)

      such as :

      temp =filter(None,[1,0,False,True,3.14,-4])

      ->

      [1,True,3.14,-4]  #result is true

      def odd(x):

             return x % 2

       temp = range(10)

       show = filter(odd,temp)

       list(show)

       ->

       [1,3,5,7,9]

       <->

       list(filter(lambda x:x % 2, range(10)))

       -> [1,3,5,7,9]

       the second is map()

      list(map(lambda x:x * 2, range(5)))

     -> [0,2,4,6,8]

 

31. In python ,there are alse have recursion.

      by default ,the depth is 100 , but you can change it.

      import sys

      sys.setrecursionlimit(1000)

      def recursion():

              return recursion()

      recursion()

      now we can count a simple question:

      how to achieve 1 * 2 * 3 * 4 * 5

      def funcation(n):

              result = n

              for i in range(1, n)

                   result *= i

               return result

       print(funcation(5))

       -> 120

      now we can change a way to achieve it ,by recurtion:

      def recurtion(n):

            if n ==1: 

                return 1

            else:

                return n * recurtion(n-1)

       print(recurtion(5))

       -> 120

      we can see another question, how to achieve :1, 1, 2, 3, 5, 8, 13, 21

      as you know ,the regular is :

      f(1) = 1,

      f(2) = 1,

      f(n) = f(n-1)+f(n-2)

      def funcation(n):

             if n == 1 or n == 2:

                  return 1

             else:

                   return funcation(n - 1) * funcation(n - 2)

       print(funcation(6))

       -> 8

       now we see a classic question hanoi:

       def hanoi:(n,x,y,z):

            if n == 1:

                  print(x,'->,z)

            else:

                  hanoi(n-1,x,z,y)

                  print(x,'->',z)

                  hanoi(n-1,y,x,z)