What are the reserved words in Python?

What are the reserved words in Python? Let me introduce to you a summary of Python’s 33 reserved words:

1 false

#Boolean type value, indicating false, corresponding to true

2 class　

#Keywords for defining classes

##3 finally　

#Exception The keyword used in processing can be used to specify the code that is always executed. The specified code is in finally

For example: 　　　

class MyException(Exception):pass　　　　　　
try:　　　　　　　　
    #some code here　　　　　　　　
    raise MyException　　　　　　
except MyException:　　　　　　　　
    print "MyException encoutered"　　　　　　
finally:　　　　　　　　
    print "Arrive finally"

4 is　

# Objects in Python contain three elements: id, type, value

Among them:

id: used to uniquely identify an object
type: identifies the type of the object
value: Is the value of the object
is: It is used to determine whether the a object is the b object. It is judged by the id.

==: It determines whether the value of the a object is equal to the value of the b object. It is judged by value

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For example: 　　

>>> a = 1　　　　　　
>>> b = 1.0　　　　　　
>>> a is b　　　　　　
False　　　　　　
>>> a == b
True
>>> id(a)
12777000
>>> id(b)
14986000

5 return#Python function returns the value return. There must be a return value in the function to be a complete function. If you do not define a function return value in Python, then you will get a None object as a result, and None means there is no value.

For example: None is not the empty string. Comparing None with any other data type always returns False. None has its own data type NoneType. We can copy None to any variable, but we cannot create other NoneType objects.

For example: 　　　

    def fnc1(x,y):       　　
print x+y　　　　　　
    当函数没有显示return，默认返回none值，以下测试：
　　    >>> result = fnc1(2, 3)　　　　　　　　
　　　　>>> result is None　　　　　　　　
　　　　True

7 continue　

#The continue statement is used to tell Python to skip the remaining statements in the current loop block and continue. Next cycle.

8 for

#The for loop can traverse any sequence of items, such as a list or a string

For example:

>>> type(None)  
  
>>> None == 0  
False  
>>> None == ''  
False  
>>> None == None  
True  
>>> None == False  
False

9 lambda

#Anonymous function is a very fashionable concept, which improves the simplicity of the code.

For example: ​​exists for the definition of a single-line function.

10 try

#Programmers can use the try...except statement to handle exceptions. Put the normal statement blocks in the try block, and put the error handling statements in the except block.

11 true

#A Boolean type value, indicating true, which is the opposite of false.

12 def

# used to define functions. For example:

for letter in 'Python': # 第一个实例 　　　　　　
print '当前字母 :', letter 　　　　　　

fruits = ['banana', 'apple', 'mango'] 　　　　　　
for fruit in fruits: # 第二个实例 　　　　　　
print '当前水果 :', fruit 　　　　　　
print "Good bye!"

13 from

#Use import in python Or from...import to import the corresponding module.

14 nonlocal

#The nonlocal keyword is used to use outer (non-global) variables in functions or other scopes.　　

For example:　　　

g = lambda x:x+1

15 while

#The while statement repeatedly executes a block of statements. while is a type of loop statement that has an optional else clause.
16 and

#Logical judgment statement, if both the left and right sides of and are true, then the judgment result is true, otherwise both are false
17 del

#del is used for list operations to delete one or several consecutive elements.　　

For example:　　　

g(1)
>>>2
g(2)
>>>3
g(7)
>>>8

18 global

#Define a global scalar.
19 not

#Logical judgment, the meaning of inversion
20 with

#with is available after python2.5 Yes, it is essentially a control flow statement. with can be used to simplify the try...finally statement. Its main usage is to implement a class _enter_() and _exit_() method.​​

For example:

>>> foo = [2, 18, 9, 22, 17, 24, 8, 12, 27]
>>>
>>> print filter(lambda x: x % 3 == 0, foo)
　　[18, 9, 24, 12, 27]
>>>
>>> print map(lambda x: x * 2 + 10, foo)
　　[14, 46, 28, 54, 44, 58, 26, 34, 64]
>>>
>>> print reduce(lambda x, y: x + y, foo)

21 as

# Used in conjunction with with.
22 elif

# Used with if

23 if

#if statement is used to test an Condition, if the condition is true, we run a block of statements (called if... block), otherwise we process another block of statements (called else... block). The else clause is optional.

24 or

#Logical judgment, if one of the two sides of or is true, the judgment result is true.

25 yield

#yield is used like return. Yield tells the program to require the function to return a generator

For example:

def hello()　　　　　　　　
    print('hello,hongten')　　　　　　
调用：　　　　　　
hello()　　　　　　
结果：　　　　　　
>>>hello,hongten

26 assert

#Assertion is used to check the correctness of the program during operation, and has the same function as other languages.
For example: 　　　

def make_counter():　　　　　　　　
    count = 0　　　　　　　　
    def counter():　　　　　　　　　　
        nonlocal count　　　　　　　　　　
        count += 1　　　　　　　　　　
    return count　　　　　　　　
    return counter　　　　　　
def make_counter_test():　　　　　　　　
    mc = make_counter()　　　　　　　　
    print(mc())　　　　　　　　
    print(mc())　　　　　　　　
    print(mc())

27 else
#Use with if

28 import

#at Python uses import or from...import to import the corresponding module. For example:

from sys import *　　　　　　
print（‘path’,path）

29 pass
#pass的意思是什么都不要做，作用是为了弥补语法和空定义上的冲突，它的好处体现在代码的编写过程之中，比如你可以先写好软件的整个框架，然后再填好框架内具体函数和class的内容，如果没有pass编译器会报一堆的错误，让整个开发很不流畅。
例如：　　　　　　

def f(arg): pass # a function that does nothing (yet)　　　　　　
class C: pass    # a class with no methods(yet)

30 break
#break语句是用来终止循环语句的，即使哪怕循环条件没有称为false或者序列还没有被完全递归，也会停止循环语句。提示，如果break的是for或while循环，任何对应的循环else块将不执行。

31 except
#使用try和except语句来铺货异常。

32 in
#for…in是另外一个循环语句，它在一序列的对象上递归即逐一使用队列中的每个项目。

33 raise
#raise抛出异常。　　　　

例如：

class MyException(Exception):pass　　　　　　
try:　　　　　　　　
    #some code here　　　　　　　　
    raise MyException　　　　　　
except MyException:　　　　　　　　
    print('MyException encoutered')　　　　　　
finally:　　　　　　　　
    print('Arrive finally')

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