Don't overwrite built-in name; add some blank lines for readability

Doc/lib/libshelve.tex

@@ -143,15 +143,17 @@ data = d[key]   # retrieve a COPY of data at key (raise KeyError if no
 del d[key]      # delete data stored at key (raises KeyError
                 # if no such key)
 flag = d.has_key(key)   # true if the key exists
-list = d.keys() # a list of all existing keys (slow!)
+klist = d.keys() # a list of all existing keys (slow!)
 
 # as d was opened WITHOUT writeback=True, beware:
 d['xx'] = range(4)  # this works as expected, but...
 d['xx'].append(5)   # *this doesn't!* -- d['xx'] is STILL range(4)!!!
+
 # having opened d without writeback=True, you need to code carefully:
 temp = d['xx']      # extracts the copy
 temp.append(5)      # mutates the copy
 d['xx'] = temp      # stores the copy right back, to persist it
+
 # or, d=shelve.open(filename,writeback=True) would let you just code
 # d['xx'].append(5) and have it work as expected, BUT it would also
 # consume more memory and make the d.close() operation slower.