[Python-Dev] Re: Printing objects on files

Wed, 3 May 2000 02:51:30 -0700 (PDT)

On Wed, 3 May 2000, Ka-Ping Yee wrote:
>> Fantasizing about other useful kinds of state beyond "encs"
> and "floatprec" ("listmax"? "ratprec"?) and managing this
> namespace is left as an exercise to the reader.

Okay, i lied. Shortly after writing this i realized that it
is probably advisable for all such bits of state to be stored
in stacks, so an interface such as this might do:
 def push(self, key, value):
 if not self.state.has_key(key):
 self.state[key] = []
 self.state[key].append(value)
 def pop(self, key):
 if self.state.has_key(key):
 if len(self.state[key]):
 self.state[key].pop()
 def get(self, key):
 if not self.state.has_key(key):
 stack = self.state[key][-1]
 if stack:
 return stack[-1]
 return None
Thus:
 >>> print 1/3
 0.33333333333333331
 >>> sys.stdout.push("float.prec", 6)
 >>> print 1/3
 0.333333
 >>> sys.stdout.pop("float.prec")
 >>> print 1/3
 0.33333333333333331
And once we allow arbitrary strings as keys to the bits
of state, the period is a natural separator we can use
for managing the namespace.
Take the special case for Unicode out of the file object:
 
 def printout(self, x):
 x.__print__(self)
 self.write("\n")
and have the Unicode string do the work:
 def __printon__(self, file):
 file.write(self.encode(file.get("unicode.enc")))
This behaves just right if an encoding of None means ASCII.
If mucking with encodings is sufficiently common, you could
imagine conveniences on file objects such as
 def __init__(self, filename, mode, encoding=None):
 ...
 if encoding:
 self.push("unicode.enc", encoding)
 def pushenc(self, encoding):
 self.push("unicode.enc", encoding)
 def popenc(self, encoding):
 self.pop("unicode.enc")
-- ?!ng