Use functions; modernize code

Demo/zlib/minigzip.py

 #!/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=v+ (ord(input.read(1))<<16)
-    v=v+ (ord(input.read(1))<<24)
+    v = ord(input.read(1))
+    v += (ord(input.read(1)) << 8 )
+    v += (ord(input.read(1)) << 16)
+    v += (ord(input.read(1)) << 24)
     return v
 
-import zlib, sys
-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:
+def compress (filename, input, output):
     output.write('\037\213\010')        # Write the header, ...
     output.write(chr(FNAME))            # ... flag byte ...
 
-    import os                           # ... modification time ...
-    statval=os.stat(filename)
-    mtime=statval[8]
+    statval = os.stat(filename)           # ... modification time ...
+    mtime = statval[8]
     write32(output, mtime)
     output.write('\002')                # ... slowest compression alg. ...
     output.write('\377')                # ... OS (=unknown) ...
     output.write(filename+'\000')       # ... original filename ...
 
-    crcval=zlib.crc32("")
-    compobj=zlib.compressobj(9, zlib.DEFLATED, -zlib.MAX_WBITS,
+    crcval = zlib.crc32("")
+    compobj = zlib.compressobj(9, zlib.DEFLATED, -zlib.MAX_WBITS,
                              zlib.DEF_MEM_LEVEL, 0)
-    while (1):
-        data=input.read(1024)
-        if data=="": break
-        crcval=zlib.crc32(data, crcval)
+    while True:
+        data = input.read(1024)
+        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:
-    magic=input.read(2)
-    if magic!='\037\213':
-        print 'Not a gzipped file' ; sys.exit(0)
-    if ord(input.read(1))!=8:
-        print 'Unknown compression method' ; sys.exit(0)
-    flag=ord(input.read(1))
+def decompress (input, output):
+    magic = input.read(2)
+    if magic != '\037\213':
+        print 'Not a gzipped file'
+        sys.exit(0)
+    if ord(input.read(1)) != 8:
+        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 = 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):
-            s=input.read(1)
-            if s=='\000': break
+        while True:
+            s = input.read(1)
+            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):
+
+    decompobj = zlib.decompressobj(-zlib.MAX_WBITS)
+    crcval = zlib.crc32("")
+    length = 0
+    while True:
         data=input.read(1024)
-        if data=="": break
-        decompdata=decompobj.decompress(data)
-        print len(decompdata)
-        output.write(decompdata) ; length=length+len(decompdata)
-        crcval=zlib.crc32(decompdata, crcval)
-    decompdata=decompobj.flush()
-    output.write(decompdata) ; length=length+len(decompdata)
-    crcval=zlib.crc32(decompdata, crcval)
+        if data == "":
+            break
+        decompdata = decompobj.decompress(data)
+        output.write(decompdata)
+        length += len(decompdata)
+        crcval = zlib.crc32(decompdata, crcval)
+
+    decompdata = decompobj.flush()
+    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
     # to reread the 8 bytes containing the CRC and the file size.  The
     # decompressor is smart and knows when to stop, so feeding it
     # extra data is harmless.
     input.seek(-8, 2)
-    crc32=read32(input)
-    isize=read32(input)
-    if crc32!=crcval: print 'CRC check failed.'
-    if isize!=length: print 'Incorrect length of data produced'
+    crc32 = read32(input)
+    isize = read32(input)
+    if crc32 != crcval:
+        print 'CRC check failed.'
+    if isize != length:
+        print 'Incorrect length of data produced'
+
+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()
 
-input.close() ; output.close()
+if __name__ == '__main__':
+    main()