Dump .pyc file (Python 3.5 version)

pycdump.py

#                                                                                                                                                                                                           
# read a .pyc file and pretty-print it                                                                                                                                                                      
#                                                                                                                                                                                                           
# copied from http://nedbatchelder.com/blog/200804/the_structure_of_pyc_files.html                                                                                                                          
# and updated to Python 3.5 (Nov 10th 2015)                                                                                                                                                                 
#                                                                                                                                                                                                           

import dis, marshal, struct, sys, time, types, binascii

def show_file(fname):
    f = open(fname, "rb")
    magic = f.read(4)
    moddate = f.read(4)
    filesz = f.read(4)
    modtime = time.asctime(time.localtime(struct.unpack('=L', moddate)[0]))
    filesz = struct.unpack('=L', filesz)
    print ("magic %s" % (binascii.hexlify(magic)))
    print ("moddate %s (%s)" % (binascii.hexlify(moddate), modtime))
    print ("files sz %d" % filesz)
    code = marshal.load(f)
    show_code(code)

def show_code(code, indent=''):
    print ("%scode" % indent)
    indent += '   '
    print ("%sargcount %d" % (indent, code.co_argcount))
    print ("%snlocals %d" % (indent, code.co_nlocals))
    print ("%sstacksize %d" % (indent, code.co_stacksize))
    print ("%sflags %04x" % (indent, code.co_flags))
    show_hex("code", code.co_code, indent=indent)
    dis.disassemble(code)
    print ("%sconsts" % indent)
    for const in code.co_consts:
        if type(const) == types.CodeType:
            show_code(const, indent+'   ')
        else:
            print ("   %s%r" % (indent, const))
    print ("%snames %r" % (indent, code.co_names))
    print ("%svarnames %r" % (indent, code.co_varnames))
    print ("%sfreevars %r" % (indent, code.co_freevars))
    print ("%scellvars %r" % (indent, code.co_cellvars))
    print ("%sfilename %r" % (indent, code.co_filename))
    print ("%sname %r" % (indent, code.co_name))
    print ("%sfirstlineno %d" % (indent, code.co_firstlineno))
    show_hex("lnotab", code.co_lnotab, indent=indent)

def show_hex(label, h, indent):
    h = binascii.hexlify(h)
    if len(h) < 60:
        print ("%s%s %s" % (indent, label, h))
    else:
        print ("%s%s" % (indent, label))
        for i in range(0, len(h), 60):
            print ("%s   %s" % (indent, h[i:i+60]))

show_file(sys.argv[1])

python3.6.8 can also use this, but 3.7.8 cannot. It will encount
"""
Traceback (most recent call last):
File "e:\mpy\showfile.py", line 52, in
show_file(filename)
File "e:\mpy\showfile.py", line 13, in show_file
code = marshal.load(f)
ValueError: bad marshal data (unknown type code)
"""

Not sure about 3.7, but just tested 3.8 - an additional 4 bytes of header were added. Not sure what, it's all 0s in what I tested.
Inserted other = f.read(4) at line 13 (after magic) and print ("other %s" % (binascii.hexlify(other))) at 18 (after print magic)

The change was indeed made in 3.7. The second 4-byte word of the header is now a type field rather than a modification date; type 0 uses the next two words as modification date and size as before, while types 1 and 3 (in effect; the type field is described as a bitfield) use them as a 64-bit hash (of the corresponding .py source). This is to facilitate reproducible builds. See PEP 552 for details.