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Implement Tree.pformat_latex_forest #2956

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Implement Tree.pformat_latex_forest #2956

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2633e80
Document all parameters for Tree.pformat, add doctest
tyomitch Mar 5, 2022
fb8caf4
Allow custom quotes in Tree.pformat
tyomitch Mar 5, 2022
772077c
Implement Tree.pformat_latex_forest
tyomitch Mar 5, 2022
943b7bb
Ensure backwards compatibility in Tree.pformat
tyomitch Mar 31, 2022
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24 changes: 24 additions & 0 deletions nltk/test/tree.doctest
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Original file line number Diff line number Diff line change
Expand Up @@ -39,6 +39,30 @@ tree object to one of several standard tree encodings:
[.dp [.d the ] [.np dog ] ]
[.vp [.v chased ] [.dp [.d the ] [.np cat ] ] ] ]

>>> print(tree.pformat_latex_forest())
\begin{forest}
[s
[dp [d [the] ] [np [dog] ] ]
[vp [v [chased] ] [dp [d [the] ] [np [cat] ] ] ] ]
\end{forest}

More flexibility in output is available via `pformat` method:

>>> print(tree.pformat(indent=2, nodesep="=", parens=("[[","]]"), quotes=True))
[[s=
[[dp= [[d= 'the']] [[np= 'dog']]]]
[[vp= [[v= 'chased']] [[dp= [[d= 'the']] [[np= 'cat']]]]]]]]

>>> print(tree.pformat(indent=3, nodesep="=", parens="{}", quotes="[]"))
{s=
{dp= {d= [the]} {np= [dog]}}
{vp= {v= [chased]} {dp= {d= [the]} {np= [cat]}}}}

The default output format uses parentheses, no quoting, and no separator characters:

>>> print(tree.pformat(quotes=False))
(s (dp (d the) (np dog)) (vp (v chased) (dp (d the) (np cat))))

There is also a fancy ASCII art representation:

>>> tree.pretty_print()
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74 changes: 49 additions & 25 deletions nltk/tree/tree.py
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Original file line number Diff line number Diff line change
Expand Up @@ -799,7 +799,7 @@ def pprint(self, **kwargs):
stream = None
print(self.pformat(**kwargs), file=stream)

def pformat(self, margin=70, indent=0, nodesep="", parens="()", quotes=False):
def pformat(self, margin=70, indent=0, nodesep="", parens="()", quotes=("", "")):
"""
:return: A pretty-printed string representation of this tree.
:rtype: str
Expand All @@ -810,10 +810,18 @@ def pformat(self, margin=70, indent=0, nodesep="", parens="()", quotes=False):
subsequent lines.
:type indent: int
:param nodesep: A string that is used to separate the node
from the children. E.g., the default value ``':'`` gives
from the children. E.g., the value ``':'`` gives
trees like ``(S: (NP: I) (VP: (V: saw) (NP: it)))``.
:type nodesep: str
:param parens: Two-element iterable to surround non-leaf nodes.
:param quotes: Two-element iterable to surround leaf nodes,
or True to quote leaf nodes as Python strings.
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To the best of my knowledge we've avoided this kind of polymorphism in NLTK. I think it needs some consideration if we're going to start doing this.

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To the best of my knowledge we've avoided this kind of polymorphism in NLTK. I think it needs some consideration if we're going to start doing this.

Any alternative suggestions?

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Sorry for the delay...

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These changes by @tyomitch make quotes equivalent to parens, which is a logical move. Then, beyond that, he also allows backwards compatibility so True and False can still be used. I don't necessarily see an issue with that, especially because using True means the use of repr, which cleverly uses the right quotes depending on the string.

That said, at a glance the implementation is likely bugged. On line 841 - what if the child is a string, and quotes = False. Then, the if-statement is true, and "\n" + indent_str + quotes[0] + str(child) + quotes[1] is added to s. However, quotes[0] will throw an exception.

An alternative implementation that avoids the polymorphism simply reverts quotes to what it was, and adds e.g. quote_strings=None. The last else branch is where the quotes should be added, so then we can do e.g.:

            elif isinstance(child, str) and not quotes:
                s += "\n" + " " * (indent + 2) + "%s" % child
            else:
                if not quote_strings:
                    s += "\n" + " " * (indent + 2) + repr(child)
                else:
                    s += "\n" + " " * (indent + 2) + quote_strings[0] + str(child) + quote_strings[1]

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@tomaarsen thank you for the detailed comment.

My expectation is that pre-existing callers either pass quotes=True or don't pass quotes at all; that's why the updated docstring doesn't list False as an acceptable input.

With the code you suggest, when quotes is False, quote_strings get ignored, which may be confusing to the user. To apply custom quote characters, he'd need to pass both parameters, which is less user-friendly. I have no problem with that -- just flagging it up.

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I agree that that would be confusing. I don't dislike your current implementation per se, although I would probably want to see support for quotes=False (i.e. have it be equivalent to quotes=("", "")).

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@tomaarsen I've added a commit to support quotes=False

"""

# For backwards compatibility
if quotes is False:
quotes = ("", "")

# Try writing it on one line.
s = self._pformat_flat(nodesep, parens, quotes)
if len(s) + indent < margin:
Expand All @@ -824,19 +832,20 @@ def pformat(self, margin=70, indent=0, nodesep="", parens="()", quotes=False):
s = f"{parens[0]}{self._label}{nodesep}"
else:
s = f"{parens[0]}{repr(self._label)}{nodesep}"
indent_str = " " * (indent + 2)
for child in self:
if isinstance(child, Tree):
s += (
"\n"
+ " " * (indent + 2)
+ indent_str
+ child.pformat(margin, indent + 2, nodesep, parens, quotes)
)
elif isinstance(child, tuple):
s += "\n" + " " * (indent + 2) + "/".join(child)
elif isinstance(child, str) and not quotes:
s += "\n" + " " * (indent + 2) + "%s" % child
s += "\n" + indent_str + "/".join(child)
elif isinstance(child, str) and quotes is not True:
s += "\n" + indent_str + quotes[0] + str(child) + quotes[1]
else:
s += "\n" + " " * (indent + 2) + repr(child)
s += "\n" + indent_str + repr(child)
return s + parens[1]

def pformat_latex_qtree(self):
Expand All @@ -862,33 +871,48 @@ def pformat_latex_qtree(self):
pformat = self.pformat(indent=6, nodesep="", parens=("[.", " ]"))
return r"\Tree " + re.sub(reserved_chars, r"\\\1", pformat)

def pformat_latex_forest(self):
r"""
Returns a representation of the tree compatible with the
LaTeX forest package. This consists of the tree represented
in bracketed notation, wrapped in a forest environment.

For example, the following result was generated from a parse
tree of the sentence ``the dog chased the cat``::

\begin{forest}
[S
[NP [D [the] ] [N [dog] ] ]
[VP [V [chased] ] [NP [D [the] ] [N [cat] ] ] ] ]
\end{forest}

:return: A latex forest representation of this tree.
:rtype: str
"""
reserved_chars = re.compile(r"([#\$%&~_\{\}])")

pformat = self.pformat(indent=2, parens=("[", " ]"), quotes=("[", "]"))
pformat = re.sub(reserved_chars, r"\\\1", pformat)
return "\\begin{forest}\n " + pformat + "\n\\end{forest}"

def _pformat_flat(self, nodesep, parens, quotes):
childstrs = []
for child in self:
if isinstance(child, Tree):
childstrs.append(child._pformat_flat(nodesep, parens, quotes))
elif isinstance(child, tuple):
childstrs.append("/".join(child))
elif isinstance(child, str) and not quotes:
childstrs.append("%s" % child)
elif isinstance(child, str) and quotes is not True:
childstrs.append(f"{quotes[0]}{child}{quotes[1]}")
else:
childstrs.append(repr(child))
if isinstance(self._label, str):
return "{}{}{} {}{}".format(
parens[0],
self._label,
nodesep,
" ".join(childstrs),
parens[1],
)
else:
return "{}{}{} {}{}".format(
parens[0],
repr(self._label),
nodesep,
" ".join(childstrs),
parens[1],
)
return "{}{}{} {}{}".format(
parens[0],
self._label if isinstance(self._label, str) else repr(self._label),
nodesep,
" ".join(childstrs),
parens[1],
)


def _child_names(tree):
Expand Down