Use functions; modernize code

Demo/zlib/minigzip.py

@@ -1,40 +1,32 @@
 #!/usr/bin/env python
 # Demo program for zlib; it compresses or decompresses files, but *doesn't*
 # delete the original.  This doesn't support all of gzip's options.
+#
+# The 'gzip' module in the standard library provides a more complete
+# implementation of gzip-format files.
+
+import zlib, sys, os
 
 FTEXT, FHCRC, FEXTRA, FNAME, FCOMMENT = 1, 2, 4, 8, 16
 
 def write32(output, value):
-    output.write(chr(value & 255)) ; value=value / 256
+    output.write(chr(value & 255)) ; value=value // 256
-    output.write(chr(value & 255)) ; value=value / 256
+    output.write(chr(value & 255)) ; value=value // 256
-    output.write(chr(value & 255)) ; value=value / 256
+    output.write(chr(value & 255)) ; value=value // 256
     output.write(chr(value & 255))
 
 def read32(input):
     v = ord(input.read(1))
-    v=v+ (ord(input.read(1))<<8 )
+    v += (ord(input.read(1)) << 8 )
-    v=v+ (ord(input.read(1))<<16)
+    v += (ord(input.read(1)) << 16)
-    v=v+ (ord(input.read(1))<<24)
+    v += (ord(input.read(1)) << 24)
     return v
 
-import zlib, sys
+def compress (filename, input, output):
-if len(sys.argv)!=2:
-    print 'Usage: minigzip.py <filename>'
-    print '  The file will be compressed or decompressed.'
-    sys.exit(0)
-
-filename=sys.argv[1]
-compressing=1 ; outputname=filename+'.gz'
-if filename[-3:]=='.gz':
-    compressing=0 ; outputname=filename[:-3]
-input=open(filename) ; output=open(outputname, 'w')
-
-if compressing:
     output.write('\037\213\010')        # Write the header, ...
     output.write(chr(FNAME))            # ... flag byte ...
 
-    import os                           # ... modification time ...
+    statval = os.stat(filename)           # ... modification time ...
-    statval=os.stat(filename)
     mtime = statval[8]
     write32(output, mtime)
     output.write('\002')                # ... slowest compression alg. ...
@@ -44,53 +36,60 @@ if compressing:
     crcval = zlib.crc32("")
     compobj = zlib.compressobj(9, zlib.DEFLATED, -zlib.MAX_WBITS,
                              zlib.DEF_MEM_LEVEL, 0)
-    while (1):
+    while True:
         data = input.read(1024)
-        if data=="": break
+        if data == "":
+            break
         crcval = zlib.crc32(data, crcval)
         output.write(compobj.compress(data))
     output.write(compobj.flush())
     write32(output, crcval)             # ... the CRC ...
     write32(output, statval[6])         # and the file size.
 
-else:
+def decompress (input, output):
     magic = input.read(2)
     if magic != '\037\213':
-        print 'Not a gzipped file' ; sys.exit(0)
+        print 'Not a gzipped file'
+        sys.exit(0)
     if ord(input.read(1)) != 8:
-        print 'Unknown compression method' ; sys.exit(0)
+        print 'Unknown compression method'
+        sys.exit(0)
     flag = ord(input.read(1))
     input.read(4+1+1)                   # Discard modification time,
                                         # extra flags, and OS byte.
     if flag & FEXTRA:
         # Read & discard the extra field, if present
         xlen = ord(input.read(1))
-        xlen=xlen+256*ord(input.read(1))
+        xlen += 256*ord(input.read(1))
         input.read(xlen)
     if flag & FNAME:
         # Read and discard a null-terminated string containing the filename
-        while (1):
+        while True:
             s = input.read(1)
-            if s=='\000': break
+            if s == '\0': break
     if flag & FCOMMENT:
         # Read and discard a null-terminated string containing a comment
-        while (1):
+        while True:
             s=input.read(1)
-            if s=='\000': break
+            if s=='\0': break
     if flag & FHCRC:
         input.read(2)                   # Read & discard the 16-bit header CRC
+
     decompobj = zlib.decompressobj(-zlib.MAX_WBITS)
     crcval = zlib.crc32("")
     length = 0
-    while (1):
+    while True:
         data=input.read(1024)
-        if data=="": break
+        if data == "":
+            break
         decompdata = decompobj.decompress(data)
-        print len(decompdata)
+        output.write(decompdata)
-        output.write(decompdata) ; length=length+len(decompdata)
+        length += len(decompdata)
         crcval = zlib.crc32(decompdata, crcval)
+
     decompdata = decompobj.flush()
-    output.write(decompdata) ; length=length+len(decompdata)
+    output.write(decompdata)
+    length += len(decompdata)
     crcval = zlib.crc32(decompdata, crcval)
 
     # We've read to the end of the file, so we have to rewind in order
@@ -100,7 +99,35 @@ else:
     input.seek(-8, 2)
     crc32 = read32(input)
     isize = read32(input)
-    if crc32!=crcval: print 'CRC check failed.'
+    if crc32 != crcval:
-    if isize!=length: print 'Incorrect length of data produced'
+        print 'CRC check failed.'
+    if isize != length:
+        print 'Incorrect length of data produced'
 
-input.close() ; output.close()
+def main():
+    if len(sys.argv)!=2:
+        print 'Usage: minigzip.py <filename>'
+        print '  The file will be compressed or decompressed.'
+        sys.exit(0)
+
+    filename = sys.argv[1]
+    if filename.endswith('.gz'):
+        compressing = False
+        outputname = filename[:-3]
+    else:
+        compressing = True
+        outputname = filename + '.gz'
+
+    input = open(filename, 'rb')
+    output = open(outputname, 'wb')
+
+    if compressing:
+        compress(filename, input, output)
+    else:
+        decompress(input, output)
+
+    input.close()
+    output.close()
+
+if __name__ == '__main__':
+    main()