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#!/usr/bin/env python3
# Change the #! line occurring in Python scripts. The new interpreter
# pathname must be given with a -i option.
#
# Command line arguments are files or directories to be processed.
# Directories are searched recursively for files whose name looks
# like a python module.
# Symbolic links are always ignored (except as explicit directory
# arguments).
# The original file is kept as a back-up (with a "~" attached to its name),
# -n flag can be used to disable this.
#
# Undoubtedly you can do this using find and sed or perl, but this is
# a nice example of Python code that recurses down a directory tree
# and uses regular expressions. Also note several subtleties like
# preserving the file's mode and avoiding to even write a temp file
# when no changes are needed for a file.
#
# NB: by changing only the function fixfile() you can turn this
# into a program for a different change to Python programs...
import sys
import re
import os
from stat import *
import getopt
err = sys.stderr.write
dbg = err
rep = sys.stdout.write
new_interpreter = None
preserve_timestamps = False
create_backup = True
def main():
global new_interpreter
global preserve_timestamps
global create_backup
usage = ('usage: %s -i /interpreter -p -n file-or-directory ...\n' %
sys.argv[0])
try:
opts, args = getopt.getopt(sys.argv[1:], 'i:pn')
except getopt.error as msg:
err(str(msg) + '\n')
err(usage)
sys.exit(2)
for o, a in opts:
if o == '-i':
new_interpreter = a.encode()
if o == '-p':
preserve_timestamps = True
if o == '-n':
create_backup = False
if not new_interpreter or not new_interpreter.startswith(b'/') or \
not args:
err('-i option or file-or-directory missing\n')
err(usage)
sys.exit(2)
bad = 0
for arg in args:
if os.path.isdir(arg):
if recursedown(arg): bad = 1
elif os.path.islink(arg):
err(arg + ': will not process symbolic links\n')
bad = 1
else:
if fix(arg): bad = 1
sys.exit(bad)
ispythonprog = re.compile(r'^[a-zA-Z0-9_]+\.py$')
def ispython(name):
return bool(ispythonprog.match(name))
def recursedown(dirname):
dbg('recursedown(%r)\n' % (dirname,))
bad = 0
try:
names = os.listdir(dirname)
except OSError as msg:
err('%s: cannot list directory: %r\n' % (dirname, msg))
return 1
names.sort()
subdirs = []
for name in names:
if name in (os.curdir, os.pardir): continue
fullname = os.path.join(dirname, name)
if os.path.islink(fullname): pass
elif os.path.isdir(fullname):
subdirs.append(fullname)
elif ispython(name):
if fix(fullname): bad = 1
for fullname in subdirs:
if recursedown(fullname): bad = 1
return bad
def fix(filename):
## dbg('fix(%r)\n' % (filename,))
try:
f = open(filename, 'rb')
except IOError as msg:
err('%s: cannot open: %r\n' % (filename, msg))
return 1
with f:
line = f.readline()
fixed = fixline(line)
if line == fixed:
rep(filename+': no change\n')
return
head, tail = os.path.split(filename)
tempname = os.path.join(head, '@' + tail)
try:
g = open(tempname, 'wb')
except IOError as msg:
err('%s: cannot create: %r\n' % (tempname, msg))
return 1
with g:
rep(filename + ': updating\n')
g.write(fixed)
BUFSIZE = 8*1024
while 1:
buf = f.read(BUFSIZE)
if not buf: break
g.write(buf)
# Finishing touch -- move files
mtime = None
atime = None
# First copy the file's mode to the temp file
try:
statbuf = os.stat(filename)
mtime = statbuf.st_mtime
atime = statbuf.st_atime
os.chmod(tempname, statbuf[ST_MODE] & 0o7777)
except OSError as msg:
err('%s: warning: chmod failed (%r)\n' % (tempname, msg))
# Then make a backup of the original file as filename~
if create_backup:
try:
os.rename(filename, filename + '~')
except OSError as msg:
err('%s: warning: backup failed (%r)\n' % (filename, msg))
else:
try:
os.remove(filename)
except OSError as msg:
err('%s: warning: removing failed (%r)\n' % (filename, msg))
# Now move the temp file to the original file
try:
os.rename(tempname, filename)
except OSError as msg:
err('%s: rename failed (%r)\n' % (filename, msg))
return 1
if preserve_timestamps:
if atime and mtime:
try:
os.utime(filename, (atime, mtime))
except OSError as msg:
err('%s: reset of timestamp failed (%r)\n' % (filename, msg))
return 1
# Return success
return 0
def fixline(line):
if not line.startswith(b'#!'):
return line
if b"python" not in line:
return line
return b'#! ' + new_interpreter + b'\n'
if __name__ == '__main__':
main()
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