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)