Python Basics---simple syntax

1.if statements

>> A = 10
>> B = 20
>> if (a>b):
Print ("a max!")
Else
Print ("b max!")

b max!

>> student = "Zhangxiaoyu"
>> if (student = = "Zhanxgiaoyu"):
Print ("YES")
Else
Print ("NO")

NO

>> if (Student! = "Zhanxgiaoyu"):
Print ("YES")
Else
Print ("NO")

YES
"In and not" represents the contained relationship "

>> hi = "Hello python"
>> if ("H" in hi):
Print ("Yes")
Else
Print ("No")

Yes

>> if ("" in hi):
Print ("Yes")
Else
Print ("No")

Yes

>> if ("I" in hi):
Print ("Yes")
Else
Print ("No")

No

"If statement can be Boolean type judged"

>> A = True
>> If a:
Print ("A is True")
Else
Print ("A is no True")

A is True

2.for statements

>> names = ["Xiaoyu", "Xiaowen", "Huahua", "Qiongge"]
>> for name in names:
Print (name)

Xiaoyu
Xiaowen
Huahua
Qiongge

>> for name in names:
Print (name)
if (name = = "Huahua"):
Print ("Yes")
Break

Xiaoyu
Xiaowen
Huahua
Yes

>> for name in names:
Print (name)
if (name = = "Huahua"):
Print ("Yes")
Continue

Xiaoyu
Xiaowen
Huahua
Yes
Qiongge

Range () function: zero-based looping by default, or you can set the start position and step size

>> for I in range (10):
Print (i)

01
2
3
4
5
6
7
8
9

>> for I in Range (1,20,5):
Print (i)

1
6
11
16
3. Arrays and dictionaries
(1) array

>> lists = [1,2,3,4,5,6, ' a ']
>> Lists[0]
1
>> Lists[6]
A
>> lists[6] = ' n '
>> Lists[6]
N
>> lists.append ("V")
>> lists
[1, 2, 3, 4, 5, 6, ' n ', ' V ']
(2) Dictionary
>> ret = {"Usenames": "Xiaoyu", "Password": "12345"}
>> Ret.keys ()
Dict_keys ([' Password ', ' usenames '])
>> ret.values ()
Dict_values ([' 12345 ', ' Xiaoyu '])
>> Ret.items ()
Dict_items ([' Password ', ' 12345 '), (' Usenames ', ' Xiaoyu ')])
4. Functions, classes, and methods
(1) function
def keyword to define the function.
>> def add (A, B):
Print (A+B)

>> add
3
>> sum = add
3
>> def add (A, B):
Return (A+B)
>> Add (1,9)
10

If you do not want to pass arguments when calling the Add () function, you can set the default parameters.

>> def add (a = 1,b = 9):
Return (A+B)
>> Add ()
10
>> Add (10,20)
30
(2) Classes and methods
Class A (object):
def add (self,a,b):
Return (A+B)

Count = A ()
Print (Count.add (3,9))

Class A ():
def Init(self,a,b): #初始化
SELF.A = Int (a)
self.b = Int (b)

def add (self):
Return self.a+self.b

Count = A (0,0)
Print (Count.add ())
Class A (): #B继承A
def add (self, A, b):
Return (A+B)

Class B (A):
def sub (self,a,b):
Return (A-B)

Count = B ()
Print (Count.add (10,90))
Print (Count.sub (10-9,9))
5. Module (class library, module)
(1) There is a CTime () method below the time module to get the current
Import time
Print (Time.ctime ())

From time import CTime #只会用到tiem下的ctime () method
Print (CTime ())

Import time
Print (Time.ctime ())
Print (Time.sleep (2))
Print ("Hibernate two Seconds")
Print (Time.sleep (2))
Print (Time.ctime ())

From time import # "" to represent all methods below the module
Print (CTime ())
Print ("Hibernate 3 Seconds")
Print (Sleep (3))
Print (CTime ())
5. Exceptions
(1)
Try
Open ("Abc.txt", ' R ')
Except Filenotfounderror: #试图打开一个不存在的文件与目录
Print ("an exception!") ")
(2)
Try
Print (AA)
Except Nameerror: #使用一个还未赋值对象的变量
Print ("This is a name exception")
(3)
Try
Open ("Abc.txt", ' R ')
Print (AA)
Except Exception (baseexception) as msg:
Print ("This is an exception")
Print (msg)
[Errno 2] No such file or directory: ' Abc.txt '
All exception classes in Python inherit exception, so you can use it to receive all types of exceptions. Since the python2.5 version, all exceptions have a new base class of Baseexception. Exception also inherits from Baseexception.
(4) Exception and if statement mates
Try
AA = "Python"
Print (AA)
Except Exception as msg:
Print ("With exception exists")
Else
Print ("Normal output, no exception")
Try
AA = "Python"
Print (AA)
Except Exception as Meg:
Print (msg)
Finally
Print ("executes" whether or not an exception exists)

Python Basics---simple syntax