Python notes (II): lexical structure

Little knowledge , Great challenge ！ This article is participating in “ A programmer must have a little knowledge ” Creative activities .

Hello everyone , I am a A bowl week , One doesn't want to be drunk ( Internal volume ) The front end of the . If you are lucky enough to get your favor , I'm very lucky ~

Variables and types

Variable is a carrier for storing data , That is, a container . The variables in a computer are the actual data or a piece of memory space in which data is stored , The values of variables can be read and modified , This is the basis of all computers and controls . Computers include a wide variety of data types , For example, text 、 video 、 Audio and so on. .

Python Common types

• integer ：Python Can handle integer of any size , And support binary 、 octal 、 Hexadecimal notation .
• floating-point ： Floating point numbers are commonly referred to as decimals .
• String type ： A string is any text enclosed in single or double quotation marks , single quote '' Or double quotes "" String of package , And it can be written in multiple lines （ Start with three single quotes or three double quotes , Three single quotes or three double quotes ）.
• Boolean type ： Boolean is only True、False Two values , Or True, Or False.

Variable command

Define a name for each variable ,Python Command rules for variables

• Variable names are made up of letters （ The generalized Unicode character , Excluding special characters ）、 Numbers and underscores make up , The number can't start .
• Case sensitive （ uppercase a And lowercase A It's two different variables ）.
• Don't follow keywords （ Words with special meanings , I'll talk about it later ） And system reserved words （ Such as function 、 Name of module, etc ） Conflict .

Use of variables

If you define a variable and assign a value to it , You can call... Directly in the function , The following code ：

#  Integer type 
a = 123
#  floating-point 
b = 1.23
#  String type 
c = " A bowl week "
#  Boolean type 
d = True

print(a, b, c, d)
# 123 1.23  A bowl week  True
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Detect the type and conversion of variables

Detect variable types

adopt type() Function to detect the change type , The code is as follows ：

#  Integer type 
a = 123
#  floating-point 
b = 1.23
#  String type 
c = " A bowl week "
#  Boolean type 
d = True

print(type(a), type(b), type(c), type(d))
# <class 'int'> <class 'float'> <class 'str'> <class 'bool'>
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Type conversion

have access to Python The built-in functions in convert variable types , The details are as follows ：

• int()： Convert a numeric value or string to an integer , You can specify base .
• float()： Convert a string to a floating point number .
• str()： Converts the specified object to string form , You can specify the code .
• chr()： Convert the integer to the string corresponding to the encoding （ A character ）.
• ord()： The string （ A character ） Convert to the corresponding code （ Integers ）.

The sample code is as follows ：

num = 10

str = str(num)

bool = bool(str)

print(type(str))  # <class 'str'>

print(type(bool))  # <class 'bool'>
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Operator

Operator	describe
[] 、[:]	Subscript , section
**	Index
~ 、+、 -	According to the not , The sign
* 、/、 %、 //	ride , except , model , to be divisible by
+、 -	Add , reduce
>> 、<<	Move right , Move left
&	Bitwise AND
^、 `	`
<=、 < 、>、 >=	Less than or equal to , Less than , Greater than , Greater than or equal to
== 、!=	be equal to , It's not equal to
is、 is not	Identity operator
in、 not in	member operator
not、 or 、and	Logical operators
=、+=、-=、*= 、/= 、%= 、//=、**=、&=、`	= 、^=、>>=、<<=`

• The order of operators in the above table is roughly from high to low
• The identity operator is understood as yes or No
• The member operator is understood as stay perhaps be not in
• Logical operators connect Boolean types ,and It's all true , The result is true , One of them is false , Is false ;or One of them is true , It is true , If the left is true , The right will not execute （ Short circuit principle ）;not Is to take the opposite .
• The assignment operator assigns the value on the right to the variable on the left
• Of the compound assignment operator a+=b Namely a=a+b, Other similar

input Use of functions and placeholders

Use input() Function to get keyboard input ( character string ).

Place holder , As the name suggests, it is the symbol of the station inserted in the output . among

• %d Is a placeholder for integers
• %f Is a placeholder for decimals
• %s It's a string placeholder
• %% It's a percent sign （ Because the percent sign represents a placeholder , Therefore, the percentage sign in the string with placeholder must be written as %%）

aa = input(" Please enter the string ：")
bb = int(input(" Please enter an integer value ："))
cc = float(input(" Please enter a floating point number ："))

print(" This is the input string for ：%s" % aa)
print(" This is the integer entered as ：%d" % bb)
print(" This is the floating point number of the input is ：%f" % cc)
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summary

1. Understand the role of variables , Naming rules , And how it is used
2. Learned the function input()、type()、 And the use of various functions of conversion types
3. Learned Python Basic usage of operators in , The assignment operator has the lowest priority , If you don't have a thorough understanding of priorities, you can use () To increase its priority .