Is there a way to know by which Python version the .pyc file was compiled?

Question

Is there any way to know by which Python version the .pyc file was compiled?

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Answer 1

The first two bytes of the .pyc file are the magic number that tells the version of the bytecodes. The word is stored in little-endian format, and the known values are:

Python version	Decimal	Hexadecimal	Comment
Python 1.5	20121	0x994e
Python 1.5.1	20121	0x994e
Python 1.5.2	20121	0x994e
Python 1.6	50428	0x4cc4
Python 2.0	50823	0x87c6
Python 2.0.1	50823	0x87c6
Python 2.1	60202	0x2aeb
Python 2.1.1	60202	0x2aeb
Python 2.1.2	60202	0x2aeb
Python 2.2	60717	0x2ded
Python 2.3a0	62011	0x3bf2
Python 2.3a0	62021	0x45f2
Python 2.3a0	62011	0x3bf2	!
Python 2.4a0	62041	0x59f2
Python 2.4a3	62051	0x63f2
Python 2.4b1	62061	0x6df2
Python 2.5a0	62071	0x77f2
Python 2.5a0	62081	0x81f2	ast-branch
Python 2.5a0	62091	0x8bf2	`with`
Python 2.5a0	62092	0x8cf2	changed `WITH_CLEANUP` opcode
Python 2.5b3	62101	0x95f2	fix wrong code: `for x, in ...`
Python 2.5b3	62111	0x9ff2	fix wrong code: `x += yield`
Python 2.5c1	62121	0xa9f2	fix wrong lnotab with for loops and storing constants that should have been removed
Python 2.5c2	62131	0xb3f2	fix wrong code: `for x, in ...` in listcomp/genexp
Python 2.6a0	62151	0xc7f2	peephole optimizations and `STORE_MAP` opcode
Python 2.6a1	62161	0xd1f2	`WITH_CLEANUP` optimization
Python 2.7a0	62171	0xdbf2	optimize list comprehensions/change `LIST_APPEND`
Python 2.7a0	62181	0xe5f2	optimize conditional branches: introduce `POP_JUMP_IF_FALSE` and `POP_JUMP_IF_TRUE`
Python 2.7a0	62191	0xeff2	introduce `SETUP_WITH`
Python 2.7a0	62201	0xf9f2	introduce `BUILD_SET`
Python 2.7a0	62211	0x03f3	introduce `MAP_ADD` and `SET_ADD`
Python 3000	3000	0xb80b
	3010	0xc20b	removed `UNARY_CONVERT`
	3020	0xcc0b	added `BUILD_SET`
	3030	0xd60b	added keyword-only parameters
	3040	0xe00b	added signature annotations
	3050	0xea0b	`print` becomes a function
	3060	0xf40b	PEP 3115 metaclass syntax
	3061	0xf50b	string literals become unicode
	3071	0xff0b	PEP 3109 raise changes
	3081	0x090c	PEP 3137 make `__file__` and `__name__` unicode
	3091	0x130c	kill str8 interning
	3101	0x1d0c	merge from 2.6a0, see 62151
	3103	0x1f0c	`__file__` points to source file
Python 3.0a4	3111	0x270c	`WITH_CLEANUP` optimization
Python 3.0a5	3131	0x3b0c	lexical exception stacking, including `POP_EXCEPT`
Python 3.1a0	3141	0x450c	optimize list, set and dict comprehensions: change `LIST_APPEND` and `SET_ADD`, add `MAP_ADD`
Python 3.1a0	3151	0x4f0c	optimize conditional branches: introduce `POP_JUMP_IF_FALSE` and `POP_JUMP_IF_TRUE`
Python 3.2a0	3160	0x580c	add `SETUP_WITH`, tag: cpython-32
Python 3.2a1	3170	0x620c	add `DUP_TOP_TWO`, remove `DUP_TOPX` and `ROT_FOUR`, tag: cpython-32
Python 3.2a2	3180	0x6c0c	add `DELETE_DEREF`

Sources:

Python/import.c – merged by aix from Python 2.7.2 and Python 3.2.2
Little endian hex values for comparison first two bytes of Igor Popov’s method added by jimbob

Answered By: NPE

Answer 2

You can get the magic number of your Python as follows:

$ python -V
Python 2.6.2
# python
>>> import imp
>>> imp.get_magic().encode('hex')
'd1f20d0a'

To get the magic number for a pyc file you can do the following:

>>> f = open('test25.pyc')
>>> magic = f.read(4)
>>> magic.encode('hex')
'b3f20d0a'
>>> f = open('test26.pyc')
>>> magic = f.read(4)
>>> magic.encode('hex')
'd1f20d0a'

By comparing the magic numbers you’ll know the python version that generated the pyc file.

Answered By: Igor Popov

Answer 3

Take a look at my script in Python that detects and returns the version of Python by which the file (*.pyc or *.pyo) was compiled.

It detects versions of Python from Python 1.5 up to last Python 3 build.

Answered By: Delimitry

Answer 4

Or, if you have a GNU/Linux system you can use the command “file” in a terminal:

$ file code.pyc
> code.pyc: python 3.5.2 byte-compiled

Answered By: Tom

Answer 5

The official Python github repository no longer appears to keep the list in import.c.

When searching for a more current list than I could find elsewhere, I encountered what appears to be an up-to-date list from Google as of May 2017.

https://github.com/google/pytype/blob/master/pytype/pyc/magic.py

Answered By: Ubuntourist

Answer 6

Adding to @Igor Popov’s answer.

To check the version of the compiled script from a newer version of Python:

# written in python3

filename = "outfit.cpython-39.pyc"

with open(filename,'rb') as f:
    magic = f.read(4)

print(int.from_bytes(magic[:2], 'little'))

You can lookup the output number here:
https://github.com/google/pytype/blob/master/pytype/pyc/magic.py

Answered By: khan

Is there a way to know by which Python version the .pyc file was compiled?

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