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# Author: Fred L. Drake, Jr.
# fdrake@cnri.reston.va.us, fdrake@acm.org
#
# This is a simple little module I wrote to make life easier. I didn't
# see anything quite like it in the library, though I may have overlooked
# something. I wrote this when I was trying to read some heavily nested
# tuples with fairly non-descriptive content. This is modelled very much
# after Lisp/Scheme - style pretty-printing of lists. If you find it
# useful, thank small children who sleep at night.
"""Support to pretty-print lists, tuples, & dictionaries recursively.
Very simple, but useful, especially in debugging data structures.
Classes
-------
PrettyPrinter()
Handle pretty-printing operations onto a stream using a configured
set of formatting parameters.
Functions
---------
pformat()
Format a Python object into a pretty-printed representation.
pprint()
Pretty-print a Python object to a stream [default is sys.sydout].
saferepr()
Generate a 'standard' repr()-like value, but protect against recursive
data structures.
"""
from types import DictType, ListType, TupleType
try:
from cStringIO import StringIO
except ImportError:
from StringIO import StringIO
def pprint(object, stream=None):
"""Pretty-print a Python object to a stream [default is sys.sydout]."""
printer = PrettyPrinter(stream=stream)
printer.pprint(object)
def pformat(object):
"""Format a Python object into a pretty-printed representation."""
return PrettyPrinter().pformat(object)
def saferepr(object):
"""Version of repr() which can handle recursive data structures."""
return _safe_repr(object, {})
class PrettyPrinter:
def __init__(self, indent=1, width=80, depth=None, stream=None):
"""Handle pretty printing operations onto a stream using a set of
configured parameters.
indent
Number of spaces to indent for each level of nesting.
width
Attempted maximum number of columns in the output.
depth
The maximum depth to print out nested structures.
stream
The desired output stream. If omitted (or false), the standard
output stream available at construction will be used.
"""
assert (not depth) or depth > 0, "depth may not be negative"
assert int(indent) or 1
assert int(width) or 1
self.__depth = depth
self.__indent_per_level = indent
self.__width = width
if stream:
self.__stream = stream
else:
import sys
self.__stream = sys.stdout
def pprint(self, object):
self.__stream.write(self.pformat(object) + "\n")
def pformat(self, object):
sio = StringIO()
self.__format(object, sio, 0, 0, {}, 0)
return sio.getvalue()
def __format(self, object, stream, indent, allowance, context, level):
level = level + 1
if context.has_key(id(object)):
object = _Recursion(object)
rep = self.__repr(object, context, level - 1)
objid = id(object)
context[objid] = 1
typ = type(object)
sepLines = len(rep) > (self.__width - 1 - indent - allowance)
if sepLines and typ in (ListType, TupleType):
# Pretty-print the sequence.
stream.write((typ is ListType) and '[' or '(')
length = len(object)
if length:
indent = indent + self.__indent_per_level
self.__format(object[0], stream, indent, allowance + 1,
context, level)
if len(object) > 1:
for ent in object[1:]:
stream.write(',\n' + ' '*indent)
self.__format(ent, stream, indent,
allowance + 1, context, level)
indent = indent - self.__indent_per_level
stream.write(((typ is ListType) and ']') or ')')
elif sepLines and typ is DictType:
stream.write('{')
length = len(object)
if length:
indent = indent + self.__indent_per_level
items = object.items()
items.sort()
key, ent = items[0]
rep = self.__repr(key, context, level) + ': '
stream.write(rep)
self.__format(ent, stream, indent + len(rep),
allowance + 1, context, level)
if len(items) > 1:
for key, ent in items[1:]:
rep = self.__repr(key, context, level) + ': '
stream.write(',\n' + ' '*indent + rep)
self.__format(ent, stream, indent + len(rep),
allowance + 1, context, level)
indent = indent - self.__indent_per_level
stream.write('}')
else:
stream.write(rep)
del context[objid]
def __repr(self, object, context, level):
return _safe_repr(object, context, self.__depth, level)
def _safe_repr(object, context, maxlevels=None, level=0):
level = level + 1
typ = type(object)
if not (typ in (DictType, ListType, TupleType) and object):
return `object`
if context.has_key(id(object)):
return `_Recursion(object)`
objid = id(object)
context[objid] = 1
if typ is DictType:
if maxlevels and level >= maxlevels:
s = "{...}"
else:
items = object.items()
k, v = items[0]
s = "{%s: %s" % (_safe_repr(k, context, maxlevels, level),
_safe_repr(v, context, maxlevels, level))
for k, v in items[1:]:
s = "%s, %s: %s" \
% (s, _safe_repr(k, context, maxlevels, level),
_safe_repr(v, context, maxlevels, level))
s = s + "}"
else:
s, term = (typ is ListType) and ('[', ']') or ('(', ')')
if maxlevels and level >= maxlevels:
s = s + "..."
else:
s = s + _safe_repr(object[0], context, maxlevels, level)
for ent in object[1:]:
s = "%s, %s" % (s, _safe_repr(ent, context, maxlevels, level))
s = s + term
del context[objid]
return s
class _Recursion:
# represent a recursive relationship; really only used for the __repr__()
# method...
def __init__(self, object):
self.__repr = "<Recursion on %s with id=%s>" \
% (type(object).__name__, id(object))
def __repr__(self):
return self.__repr
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