Python Basics (variables, character encodings, data types)

Variable

The variable name consists of a letter, a number (not the first character), an underscore, and cannot use the keyword

The following keywords cannot be declared as variable names [' and ', ' as ', ' assert ', ' Break ', ' class ', ' Continue ', ' Def ', ' del ', ' elif ', ' Else ', ' except ', ' exec ', ' final ' Ly ', ' for ', ' from ', ' global ', ' if ', ' import ', ' in ', ' was ', ' lambda ', ' not ', ' or ', ' pass ', ' print ', ' raise ', ' return ', ' Try ' , ' while ', ' with ', ' yield ']

ID (variable) Gets the address of the variable

Type (variable) to get the variable's kind, type (class) Gets the path of the class

Del Delete a variable

List of special variables: sys.argv[n]

__NAME__: The value of the current file execution is main, and the value is the module name when it is called

Character encoding

1 bits is the smallest representation unit in a computer, and 1 bytes is the smallest storage unit in a computer.

8bits = 1Byte = 1 bytes

1024Bytes = 1KB = 1024 bytes

1024KB = 1MB = 1 million byte = 1 million character = 1 MB

1024MB = 1GB

...

ASCII 256 Each character occupies 8 bits

Unicode Universal Code
utf-32 = 4 bytes
utf-16 = 2 bytes
Utf-8 = 8bits Variable length encoding
English one byte, all Chinese 3 bytes
Europe 2 bytes

Data type numeric type and string type

Numeric type: can only hold one value once defined, cannot be changed, direct access

Category: Numeric int (int) float (float) long (long integer) complex (plural) boolean (true/false)

String type: Quotation marks contain string types (no difference between single-cited and double-cited)

String common features: Remove whitespace, index, length, split, slice

Strip () remove whitespace, or remove other characters

Slipt () split, separated by a space by default. can also be split with other characters

Len () Length slice: such as print (X[1:5]) is also Gu Tou regardless of the tail

Capitalize () Capitalize first letter

Center () Center Display for example: x= ' Hello ' Print (X.center (22, ' # '))

Count (): Count, Gu Tou regardless of the tail, count the number of characters, the space is also counted as a character

EndsWith () at what end

Satrtswith () Start with what

Find () finds the index position of the character, if it is negative, indicates that the lookup failed

Index () indexes

IsDigit () Determine if it is a number

Islower () to determine whether it is all lowercase

Isupper () to determine if it is all uppercase

Lower () convert all to lowercase

Upper () Convert all to uppercase

Isspace () Determine if it is all spaces

Istitle () to determine if it is a title (capitalized in the first letter)

Swapcase () uppercase and lowercase letters flipped

Join () connection

Replace () Replacement

Ljust () Align Left

There are two ways to format a Python string: a percent-semicolon, format-mode

Percent semicolons are relatively old, and format is a more advanced way of trying to replace old ways, both of which are now coexisting

Python Basics (variables, character encodings, data types)