The struct of Python

A struct is a built-in module in Python used to convert between a struct in C and a string in Python, typically from a file or network

1. function

(1) Convert Python data to a string in the specified format (the string is a byte stream)

(2) Convert a byte stream to a python-specified data type in the specified format

(3) Processing binary data, if using a struct to process the file, you need to use ' WB '/' RB ' in binary write, read the way to process the file

(4) To deal with the structure in C language

2. Common methods of struct

(1) pack (FMT, V1, v2, ...), bytes

Converts data to a string (byte stream) in the given format

(2) Pack_into (FMT, buffer, offset, v1, v2, ...)

Converts the data to a string (byte stream) in the given format and writes the byte stream to buffer starting at offset

(3) unpack (FMT, buffer) (v1, v2, ...)

Parses a byte stream and returns the result in the given format

(4) unpack_from (fmt, buffer, offset=0) (v1, v2, ...)

Resolves the buffer starting with offset in the specified format and returns the parse result

(5) calcsize (FMT), Integer

Calculates how many bytes of memory a given format takes, and note the alignment

3. Format characters

Formatting strings: Specifying data types, controlling byte order, size, and alignment

The following 2 sheets are from the official website

Character	Byte Order	Size	Alignment
@	Native	Native	Enough for 4 bytes.
=	Native	Standard	By original number of bytes
<	Little-endian	Standard	By original number of bytes
>	Big-endian	Standard	By original number of bytes
!	Network (= Big-endian)	Standard	By original number of bytes

Standard

Format	C Type	Python Type	size	Notes
x	Pad byte	No value
c	char	string of length 1	1
b	signed char	Integer	1	(3)
B	unsigned char	Integer	1	(3)
?	_Bool	bool	1	(1)
h	short	Integer	2	(3)
H	unsigned short	Integer	2	(3)
i	int	Integer	4	(3)
I	unsigned int	Integer	4	(3)
l	long	Integer	4	(3)
L	unsigned long	Integer	4	(3)
q	long long	Integer	8	(2), (3)
Q	unsigned long long	Integer	8	(2), (3)
f	float	Float	4	(4)
d	double	Float	8	(4)
s	char[]	String
p	char[]	String
P	void *	Integer		(5), (3)

4. Example

#Coding=utf-8" "struct implements read and write binary files" "ImportSYSImportstructdefWriteFile (path): Name= b"Zhanglin" Age= 30Sex= b"female"Profession= b"IT"    Try: With open (path,"WB") as Pf:text= Struct.pack (">8si6s2s", Name,age,sex,profession) pf.write (text)Print("Write file success!")    exceptException as E:Print("Write file faild!:", E)defReadFile (path): Text=NoneTry: With open (path,"RB") as Pf:text=Pf.read ()Print("Read File success!")            Print(text)Print(Struct.unpack (">8si6s2s", text)) exceptException as E:Print("Read file faild!:", E)if __name__=="__main__": Path= Sys.argv[1] WriteFile (path) ReadFile (path)

Output Result:
　　>>> D:\pystu>python struct_test.py Struct_test.txt
>>> Write File success!
>>> Read File success!
>>> B ' Zhanglin\x00\x00\x00\x1efemaleit '
>>> (b ' Zhanglin ', b ' female ', B ' IT ')

The struct of Python