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Python notes (II): lexical structure
2022-01-30 10:44:04 【A bowl week】
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
FalseTwo values , Or
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
AIt'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 Copy code
Detect the type and conversion of variables
Detect variable types
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'> Copy code
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'> Copy code
||Subscript , section|
||According to the not , The sign|
||ride , except , model , to be divisible by|
||Add , reduce|
||Move right , Move left|
||Less than or equal to , Less than , Greater than , Greater than or equal to|
||be equal to , It's not equal to|
- The order of operators in the above table is roughly from high to low
- The identity operator is understood as
- The member operator is understood as
be not in
- Logical operators connect Boolean types ,
andIt's all true , The result is true , One of them is false , Is false ;
orOne of them is true , It is true , If the left is true , The right will not execute （ Short circuit principle ）;
notIs 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=a+b, Other similar
input Use of functions and placeholders
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
%dIs a placeholder for integers
%fIs a placeholder for decimals
%sIt'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) Copy code
- Understand the role of variables , Naming rules , And how it is used
- Learned the function
type()、 And the use of various functions of conversion types
- 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 .
author[A bowl week],Please bring the original link to reprint, thank you.
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