Python struct read binary file
Show Source code: Lib/struct.py This module performs conversions between Python values and C structs represented as Python Note By default, the result of packing a given C struct includes pad bytes in order to maintain proper alignment for the C types involved; similarly, alignment is
taken into account when unpacking. This behavior is chosen so that the bytes of a packed struct correspond exactly to the layout in memory of the corresponding C struct. To handle platform-independent data formats or omit implicit pad bytes, use Several
Functions and Exceptions¶The module defines the following exception and functions: exceptionstruct. error ¶Exception raised on various occasions; argument is a string describing what is wrong. struct. pack (format, v1, v2,
...)¶Return a bytes object containing the values v1, v2, … packed according to the format string format. The arguments must match the values required by the format exactly. struct. pack_into (format, buffer, offset, v1,
v2, ...)¶Pack the values v1, v2, … according to the format string format and write the packed bytes into the writable buffer buffer starting at position offset. Note that offset is a required argument. struct. unpack (format, buffer)¶Unpack from the buffer buffer (presumably packed by struct. unpack_from (format, /, buffer, offset=0)¶Unpack from buffer starting at position offset, according to the format string format. The result is a tuple even if it contains exactly one item. The buffer’s size in bytes, starting at position offset, must be at least the size required by the format, as reflected by struct. iter_unpack (format, buffer)¶Iteratively unpack from the buffer buffer according to the format string format. This function returns an iterator which will read equally sized chunks from the buffer until all its contents have been consumed.
The buffer’s size in bytes must be a multiple of the size required by the format, as reflected by Each iteration yields a tuple as specified by the format string. New in version 3.4. struct. calcsize (format)¶Return the size of the struct (and hence of the bytes object produced by Format Strings¶Format strings are the mechanism used to specify the expected layout when packing and unpacking data. They are built up from Format Characters, which specify the type of data being packed/unpacked. In addition, there are special characters for controlling the Byte Order, Size, and Alignment. Byte Order, Size, and Alignment¶By default, C types are represented in the machine’s native format and byte order, and properly aligned by skipping pad bytes if necessary (according to the rules used by the C compiler). Alternatively, the first character of the format string can be used to indicate the byte order, size and alignment of the packed data, according to the following table:
If the first character is not one of these, Native byte order is big-endian or little-endian, depending on the host system. For example, Intel x86 and AMD64 (x86-64) are little-endian; IBM z and most legacy architectures are big-endian; and ARM, RISC-V and IBM Power feature switchable endianness (bi-endian, though the former two are nearly always little-endian in practice). Use Native
size and alignment are determined using the C compiler’s Standard size depends only on the format character; see the table in the Format Characters section. Note the difference between The form
There is no way to indicate non-native byte order (force byte-swapping); use the appropriate choice of Notes:
Format Characters¶Format characters have the following meaning; the conversion between C and Python values should be obvious given their types. The ‘Standard size’ column refers to the size of the packed value in bytes when using standard size; that is, when the format string starts with one of
Changed in version 3.3: Added support for the Changed in version 3.6: Added support for the Notes:
A format character may be preceded by an integral repeat count.
For example, the format string Whitespace characters between formats are ignored; a count and its format must not contain whitespace though. For the When packing a value Changed in version 3.1: Previously, some of the integer formats wrapped out-of-range values and raised The For the Examples¶Note All examples assume a native byte order, size, and alignment with a big-endian machine. A basic example of packing/unpacking three integers: >>> from struct import * >>> pack('hhl', 1, 2, 3) b'\x00\x01\x00\x02\x00\x00\x00\x03' >>> unpack('hhl', b'\x00\x01\x00\x02\x00\x00\x00\x03') (1, 2, 3) >>> calcsize('hhl') 8 Unpacked fields can be named by assigning them to variables or by wrapping the result in a named tuple: >>> record = b'raymond \x32\x12\x08\x01\x08' >>> name, serialnum, school, gradelevel = unpack('<10sHHb', record) >>> from collections import namedtuple >>> Student = namedtuple('Student', 'name serialnum school gradelevel') >>> Student._make(unpack('<10sHHb', record)) Student(name=b'raymond ', serialnum=4658, school=264, gradelevel=8) The ordering of format characters may have an impact on size since the padding needed to satisfy alignment requirements is different: >>> pack('ci', b'*', 0x12131415) b'*\x00\x00\x00\x12\x13\x14\x15' >>> pack('ic', 0x12131415, b'*') b'\x12\x13\x14\x15*' >>> calcsize('ci') 8 >>> calcsize('ic') 5 The following format >>> pack('llh0l', 1, 2, 3) b'\x00\x00\x00\x01\x00\x00\x00\x02\x00\x03\x00\x00' This only works when native size and alignment are in effect; standard size and alignment does not enforce any alignment. See also Modulearray Packed binary storage of homogeneous data. Modulexdrlib Packing and unpacking of XDR data. Classes¶The
struct. Struct (format)¶Return a new Struct object which writes and
reads binary data according to the format string format. Creating a Struct object once and calling its methods is more efficient than calling the Note The compiled versions of the most recent format strings passed to
Compiled Struct objects support the following methods and attributes: pack (v1, v2, ...)¶Identical to the pack_into (buffer, offset, v1, v2, ...)¶Identical to the
unpack (buffer)¶Identical to the
unpack_from (buffer,
offset=0)¶Identical to the iter_unpack (buffer)¶Identical to the
New in version 3.4. format ¶The format string used to construct this Struct object. Changed in version 3.7: The format string type is now size ¶The calculated size of the struct (and hence of the bytes object produced by the
How do I read a binary file in Python?To open a file in binary format, add 'b' to the mode parameter. Hence the "rb" mode opens the file in binary format for reading, while the "wb" mode opens the file in binary format for writing. Unlike text files, binary files are not human-readable. When opened using any text editor, the data is unrecognizable.
How do you read a binary file and convert it to the text in Python?To read the written file, I have used the same filename as document1. txt, I have used file=open(“document1. txt”,”rb”) to open the file, “rb” mode is used to read the binary file and, To read the line from the file I have used line=file. readline().. The readline() returns one line from the file.. How do you read a binary file in Python chunks?Read a Binary File in Chunks. Line [1] assigns the size of the chunk to the variable chunk_size .. Line [2] assigns the variable image_file to the file to be read in.. Line [3] opens the image_file .. Line [4] instantiates the while loop and executes while True . Line [5] reads in a chunk of the open file for each loop.. How do I read a binary file?To read from a binary file. Use the ReadAllBytes method, which returns the contents of a file as a byte array. This example reads from the file C:/Documents and Settings/selfportrait. ... . For large binary files, you can use the Read method of the FileStream object to read from the file only a specified amount at a time.. |