"""
parser and parsing-related tools
Design
------
Template string is split into tokens and the tokens are combined into
nodes. Parse tree is a nodelist. TextNode and ExpressionNode are simple
nodes and for-loop, if-loop, etc. are block nodes, which contain multi-
ple child nodes.
Each node can emit some python string. python string emitted by the root
node is validated for safeeval and executed using python in the given
environment.
Enough care is taken to make sure the generated code and the template
has line to line match, so that the error messages can point to exact
line number in template. (It still doesn't work in some cases.)
Grammar
-------
template -> defwith sections
defwith -> "$def with (" arguments ")" | ""
sections -> section*
section -> block | assignment | line
assignment -> "$ " <assignment expression>
line -> (text|expr)*
text -> <any characters other than $>
expr -> "$" pyexpr | "$(" pyexpr ")" | "${" pyexpr "}"
pyexpr -> <python expression>
"""
import collections
import re
import token
import tokenize
__all__ = ["ParseError", "SecurityError", "ForLoop"]
class Error(Exception):
""""""
class ParseError(Error):
""""""
class SecurityError(Error):
"""the template seems to be trying to do something naughty"""
_indent = " " * 4
def splitline(text):
r"""
splits `text` at first newline (modified string `partition`)
>>> splitline("foo\nbar")
('foo\n', 'bar')
>>> splitline('foo')
('foo', '')
>>> splitline("")
('', '')
"""
before, partition, after = text.partition("\n")
return before + partition, after
class Node:
""" """
class DefWith(Node):
""" """
def __init__(self, defwith, suite):
if defwith:
self.defwith = defwith.replace("with", "template__") + ":"
offset = 4 # encoding, lineoffset__, loop & self
else:
self.defwith = "def template__():"
offset = 5 # encoding, template__, lineoffset__, loop & self
self.defwith += "\n lineoffset__ = -{0}".format(offset)
self.defwith += "\n loop = ForLoop()"
self.defwith += "\n self = TemplateResult()"
self.defwith += "\n e_ = self.extend"
self.suite = suite
def emit(self, indent):
return "\n".join(
(self.defwith, self.suite.emit(indent + _indent), " return self")
)
def __repr__(self):
return "<defwith: {0}, {1}>".format(self.defwith, self.suite)
class Var(Node):
""" """
def __init__(self, name, value):
self.name = name
self.value = value
def emit(self, indent, text_indent):
return indent + "self[{0}] = {1}\n".format(repr(self.name), self.value)
def __repr__(self):
return "<var: {0} = {1}>".format(self.name, self.value)
class Text(Node):
""" """
def __init__(self, value):
self.value = value
def emit(self, indent, begin_indent=""):
return repr(self.value)
def __repr__(self):
return "t" + repr(self.value)
class Expression:
""" """
def __init__(self, value, escape=True):
self.value = value.strip()
if value.startswith("{") and value.endswith("}"): # ${...} to $(...)
self.value = "(" + self.value[1:-1] + ")"
self.escape = escape
def emit(self, indent, begin_indent=""):
return "escape_({0}, {1})".format(self.value, bool(self.escape))
def __repr__(self):
if self.escape:
escape = ""
else:
escape = ":"
return "${0}{1}".format(escape, self.value)
class Assignment:
""" """
def __init__(self, code):
self.code = code
def emit(self, indent, begin_indent=""):
return indent + self.code + "\n"
def __repr__(self):
return "<assignment: {0}>".format(repr(self.code))
class Line:
""" """
def __init__(self, nodes):
self.nodes = nodes
def emit(self, indent, text_indent="", name=""):
text = [node.emit("") for node in self.nodes]
if text_indent:
text = [repr(text_indent)] + text
return indent + "e_([{0}])\n".format(", ".join(text))
def __repr__(self):
return "<line: {0}>".format(repr(self.nodes))
class Code:
""" """
def __init__(self, stmt, block, begin_indent=""):
# compensate one line for $code:
self.code = "\n" + block
def emit(self, indent, text_indent=""):
rx = re.compile("^", re.M)
return rx.sub(indent, self.code).rstrip(" ")
def __repr__(self):
return "<code: {0}>".format(repr(self.code))
class Statement:
""" """
def __init__(self, stmt):
self.stmt = stmt
def emit(self, indent, begin_indent=""):
return indent + self.stmt
def __repr__(self):
return "<stmt: {0}>".format(repr(self.stmt))
class Suite:
"""
suite is a list of sections
"""
def __init__(self, sections):
self.sections = sections
def emit(self, indent, text_indent=""):
content = []
for section in self.sections:
content.append(section.emit(indent, text_indent))
return "\n" + "".join(content)
def __repr__(self):
return repr(self.sections)
class Block:
""" """
def __init__(self, stmt, block, begin_indent=""):
self.stmt = stmt
self.suite = Parser().read_suite(block)
self.begin_indent = begin_indent
def emit(self, indent, text_indent=""):
text_indent = self.begin_indent + text_indent
out = self.suite.emit(indent + _indent, text_indent)
return indent + self.stmt + out
def __repr__(self):
return "<block: {0}, {1}>".format(repr(self.stmt), repr(self.suite))
class Def(Block):
""" """
def __init__(self, *a, **kw):
Block.__init__(self, *a, **kw)
code = Code("", "")
code.code = "self = TemplateResult(); e_ = self.extend\n"
self.suite.sections.insert(0, code)
code = Code("", "")
code.code = "return self\n"
self.suite.sections.append(code)
def emit(self, indent, text_indent=""):
text_indent = self.begin_indent + text_indent
out = self.suite.emit(indent + _indent, text_indent)
return indent + "lineoffset__ -= 3\n" + indent + self.stmt + out
class If(Block):
pass
class Else(Block):
pass
class Elif(Block):
pass
class For(Block):
""" """
def __init__(self, stmt, block, begin_indent=""):
self.original_stmt = stmt
tok = Tokenizer(stmt)
tok.consume_till("in")
a = stmt[: tok.index] # for i in
b = stmt[tok.index : -1] # rest of for stmt excluding :
stmt = a + " loop.setup(" + b.strip() + "):"
Block.__init__(self, stmt, block, begin_indent)
def __repr__(self):
return "<block: {0}, {1}>".format(repr(self.original_stmt), repr(self.suite))
class ForLoop:
"""
wrapper for expression in for stament to support loop.xxx helpers
>>> loop = ForLoop()
>>> for x in loop.setup(["a", "b", "c"]):
... loop.index, loop.revindex, loop.parity, x
...
(1, 3, 'odd', 'a')
(2, 2, 'even', 'b')
(3, 1, 'odd', 'c')
>>> loop.index
Traceback (most recent call last):
...
AttributeError: index
"""
def __init__(self):
self._ctx = None
def __getattr__(self, name):
if self._ctx is None:
raise AttributeError(name)
else:
return getattr(self._ctx, name)
def setup(self, seq):
self._push()
return self._ctx.setup(seq)
def _push(self):
self._ctx = ForLoopContext(self, self._ctx)
def _pop(self):
self._ctx = self._ctx.parent
class ForLoopContext:
"""
stackable context for ForLoop to support nested for loops
"""
index0 = property(lambda self: self.index - 1)
first = property(lambda self: self.index == 1)
last = property(lambda self: self.index == self.length)
odd = property(lambda self: self.index % 2 == 1)
even = property(lambda self: self.index % 2 == 0)
parity = property(lambda self: ["odd", "even"][self.even])
revindex0 = property(lambda self: self.length - self.index)
revindex = property(lambda self: self.length - self.index + 1)
def __init__(self, forloop, parent):
self._forloop = forloop
self.parent = parent
def setup(self, seq):
try:
self.length = len(seq)
except:
self.length = 0
self.index = 0
for a in seq:
self.index += 1
yield a
self._forloop._pop()
class Parser:
""" """
keywords = ("pass", "break", "continue", "return")
statement_nodes = {
"for": For,
"while": Block,
"if": If,
"elif": Elif,
"else": Else,
"def": Def,
"code": Code,
}
def __init__(self):
self.statement_nodes = self.statement_nodes
self.keywords = self.keywords
def parse(self, text, name="<template>"):
self.text = text
self.name = name
defwith, text = self.read_defwith(text)
suite = self.read_suite(text)
return DefWith(defwith, suite)
def read_defwith(self, text):
if text.startswith("$def with"):
defwith, text = splitline(text)
defwith = defwith[1:].strip() # strip $ and spaces
return defwith, text
else:
return "", text
def read_section(self, text):
r"""
reads one section from the given text
section -> block | assignment | line
>>> read_section = Parser().read_section
>>> read_section("foo\nbar\n")
(<line: [t'foo\n']>, 'bar\n')
>>> read_section("$ a = b + 1\nfoo\n")
(<assignment: 'a = b + 1'>, 'foo\n')
# TODO >>> read_section("$for i in range(10):\n A $i\nB")
# TODO (<block: 'for i in range(10):', [<line: [t'A ', $i, t'\n']>]>, 'B')
"""
if text.lstrip(" ").startswith("$"):
index = text.index("$")
begin_indent, text2 = text[:index], text[index + 1 :]
ahead = self.python_lookahead(text2)
if ahead == "var":
return self.read_var(text2)
elif ahead in self.statement_nodes:
return self.read_block_section(text2, begin_indent)
elif ahead in self.keywords:
return self.read_keyword(text2)
elif ahead.strip() == "":
# assignments starts with a space after $
# ex: $ a = b + 2
return self.read_assignment(text2)
return self.readline(text)
def read_var(self, text):
r"""
reads a `var` statement
>>> read_var = Parser().read_var
>>> read_var("var x=10\nfoo")
(<var: x = 10>, 'foo')
>>> read_var("var x: hello $name\nfoo")
(<var: x = join_('hello ', escape_(name, True))>, 'foo')
"""
line, text = splitline(text)
tokens = self.python_tokens(line)
if len(tokens) < 4:
raise SyntaxError("Invalid var statement")
name = tokens[1]
sep = tokens[2]
value = line.split(sep, 1)[1].strip()
if sep == "=":
pass # no need to process value
elif sep == ":":
# FIXME hack for backward-compatability
if tokens[3] == "\n": # multi-line var statement
block, text = self.read_indented_block(text, " ")
lines = [self.readline(x)[0] for x in block.splitlines()]
_nodes = []
for x in lines:
_nodes.extend(x.nodes)
_nodes.append(Text("\n"))
else: # single-line var statement
linenode, _ = self.readline(value)
_nodes = linenode.nodes
parts = [node.emit("") for node in _nodes]
value = "join_({0})".format(", ".join(parts))
else:
raise SyntaxError("Invalid var statement")
return Var(name, value), text
def read_suite(self, text):
r"""
reads section by section till end of text
>>> read_suite = Parser().read_suite
>>> read_suite("hello $name\nfoo\n")
[<line: [t'hello ', $name, t'\n']>, <line: [t'foo\n']>]
"""
sections = []
while text:
section, text = self.read_section(text)
sections.append(section)
return Suite(sections)
def readline(self, text):
r"""
reads one line from the text
Newline is supressed if the line ends with \.
>>> readline = Parser().readline
>>> readline("hello $name!\nbye!")
(<line: [t'hello ', $name, t'!\n']>, 'bye!')
>>> readline("hello $name!\\\nbye!")
(<line: [t'hello ', $name, t'!']>, 'bye!')
>>> readline("$f()\n\n")
(<line: [$f(), t'\n']>, '\n')
"""
line, text = splitline(text)
# supress new line if line ends with \
if line.endswith("\\\n"):
line = line[:-2]
_nodes = []
while line:
node, line = self.read_node(line)
_nodes.append(node)
return Line(_nodes), text
def read_node(self, text):
r"""
reads a node from the given text and returns the node and
remaining text
>>> read_node = Parser().read_node
>>> read_node("hello $name")
(t'hello ', '$name')
>>> read_node("$name")
($name, '')
"""
if text.startswith("$$"):
return Text("$"), text[2:]
elif text.startswith("$#"): # comment
line, text = splitline(text)
return Text("\n"), text
elif text.startswith("$"):
text = text[1:] # strip $
if text.startswith(":"):
escape = False
text = text[1:] # strip `:`
else:
escape = True
return self.read_expr(text, escape=escape)
else:
return self.read_text(text)
def read_text(self, text):
r"""
reads a text node from the given text
>>> read_text = Parser().read_text
>>> read_text("hello $name")
(t'hello ', '$name')
"""
index = text.find("$")
if index < 0:
return Text(text), ""
else:
return Text(text[:index]), text[index:]
def read_keyword(self, text):
line, text = splitline(text)
return Statement(line.strip() + "\n"), text
def read_expr(self, text, escape=True):
"""
reads a python expression from the text and returns the expression
and remaining text
expr -> simple_expr | paren_expr
simple_expr -> id extended_expr
extended_expr -> attr_access | paren_expr extended_expr | ""
attr_access -> dot id extended_expr
paren_expr -> [ tokens ] | ( tokens ) | { tokens }
>>> read_expr = Parser().read_expr
>>> read_expr("name")
($name, '')
>>> read_expr("a.b and c")
($a.b, ' and c')
>>> read_expr("a. b")
($a, '. b')
>>> read_expr("name</h1>")
($name, '</h1>')
>>> read_expr("(limit)ing")
($(limit), 'ing')
>>> read_expr('a[1, 2][:3].f(1+2, "weird string[).", 3 + 4) done')
($a[1, 2][:3].f(1+2, "weird string[).", 3 + 4), ' done')
"""
parens = {"(": ")", "[": "]", "{": "}"}
def simple_expr():
identifier()
extended_expr()
def identifier():
next(tokens)
def extended_expr():
lookahead = tokens.lookahead()
if lookahead is None:
return
elif lookahead.value == ".":
attr_access()
elif lookahead.value in parens:
paren_expr()
extended_expr()
else:
return
def attr_access():
tokens.lookahead()
# XXX dot = tokens.lookahead()
if tokens.lookahead2().type == token.NAME:
next(tokens) # XXX can remove comment? -- # consume dot
identifier()
extended_expr()
def paren_expr():
begin = next(tokens).value
end = parens[begin]
while True:
if tokens.lookahead().value in parens:
paren_expr()
else:
t = next(tokens)
if t.value == end:
break
return
def get_tokens(text):
"""
tokenizes `text` using python tokenizer
Python tokenizer ignores spaces, but they might be important in
some cases. This function introduces dummy space tokens when it
identifies any ignored space. Each token is a `NamedTuple` with
attributes type, value, begin and end.
"""
readline = iter([text]).__next__
end = None
for t in tokenize.generate_tokens(readline):
t = Token(type=t[0], value=t[1], begin=t[2], end=t[3])
if end is not None and end != t.begin:
_, x1 = end
_, x2 = t.begin
yield Token(type=-1, value=text[x1:x2], begin=end, end=t.begin)
end = t.end
yield t
class BetterIter:
"""
iterator-like object with support for 2 look-aheads
"""
def __init__(self, items):
self.iteritems = iter(items)
self.items = []
self.position = 0
self.current_item = None
def lookahead(self):
if len(self.items) <= self.position:
self.items.append(self._next())
return self.items[self.position]
def _next(self):
try:
return next(self.iteritems)
except StopIteration:
return None
def lookahead2(self):
if len(self.items) <= self.position + 1:
self.items.append(self._next())
return self.items[self.position + 1]
def __next__(self):
self.current_item = self.lookahead()
self.position += 1
return self.current_item
tokens = BetterIter(get_tokens(text))
if tokens.lookahead().value in parens:
paren_expr()
else:
simple_expr()
row, col = tokens.current_item.end
return Expression(text[:col], escape=escape), text[col:]
def read_assignment(self, text):
r"""
reads assignment statement from text
>>> read_assignment = Parser().read_assignment
>>> read_assignment("a = b + 1\nfoo")
(<assignment: 'a = b + 1'>, 'foo')
"""
line, text = splitline(text)
return Assignment(line.strip()), text
def python_lookahead(self, text):
"""
returns the first python token from the given text
>>> python_lookahead = Parser().python_lookahead
>>> python_lookahead("for i in range(10):")
'for'
>>> python_lookahead("else:")
'else'
>>> python_lookahead(" x = 1")
' '
"""
readline = iter([text]).__next__
tokens = tokenize.generate_tokens(readline)
return next(tokens)[1]
def python_tokens(self, text):
readline = iter([text]).__next__
tokens = tokenize.generate_tokens(readline)
return [t[1] for t in tokens]
def read_indented_block(self, text, indent):
r"""
reads a block of text
A block is what typically follows a `for` or `if` statement. It can
be in the same line as that of the statement or an indented block.
>>> read_indented_block = Parser().read_indented_block
>>> read_indented_block(" a\n b\nc", " ")
('a\nb\n', 'c')
>>> read_indented_block(" a\n b\n c\nd", " ")
('a\n b\nc\n', 'd')
>>> read_indented_block(" a\n\n b\nc", " ")
('a\n\n b\n', 'c')
"""
if indent == "":
return "", text
block = ""
while text:
line, text2 = splitline(text)
if line.strip() == "":
block += "\n"
elif line.startswith(indent):
block += line[len(indent) :]
else:
break
text = text2
return block, text
def read_statement(self, text):
r"""
reads a python statement
>>> read_statement = Parser().read_statement
>>> read_statement("for i in range(10): hello $name")
('for i in range(10):', ' hello $name')
"""
tok = Tokenizer(text)
tok.consume_till(":")
return text[: tok.index], text[tok.index :]
def read_block_section(self, text, begin_indent=""):
r"""
TODO
>>> read_block_section = Parser().read_block_section
>>> read_block_section("for i in range(10): hi $i\nB")
(<block: 'for i in range(10):', [<line: [t'hi ', $i, t'\n']>]>, 'B')
>>> read_block_section("for i in range(10):\n hi $i\n B",
... begin_indent=" ")
(<block: 'for i in range(10):', [<line: [t'hi ', $i, t'\n']>]>, ' B')
>>> read_block_section("for i in range(10):\n hi $i\nB")
(<block: 'for i in range(10):', [<line: [t'hi ', $i, t'\n']>]>, 'B')
"""
line, text = splitline(text)
stmt, line = self.read_statement(line)
keyword = self.python_lookahead(stmt)
# if there is some thing left in the line
if line.strip():
block = line.lstrip()
else:
def find_indent(text):
rx = re.compile(" +")
match = rx.match(text)
first_indent = match and match.group(0)
return first_indent or ""
# find the indentation of the block by looking at the first line
first_indent = find_indent(text)[len(begin_indent) :]
# TODO fix this special case
if keyword == "code":
indent = begin_indent + first_indent
else:
indent = begin_indent + min(first_indent, _indent)
block, text = self.read_indented_block(text, indent)
return self.create_block_node(keyword, stmt, block, begin_indent), text
def create_block_node(self, keyword, stmt, block, begin_indent):
if keyword in self.statement_nodes:
return self.statement_nodes[keyword](stmt, block, begin_indent)
else:
raise ParseError("Unknown statement: {0}".format(repr(keyword)))
Token = collections.namedtuple("Token", "type, value, begin, end")
class Tokenizer:
"""
utility wrapper over `tokenize` token generator
"""
def __init__(self, text):
self.text = text
readline = iter([text]).__next__
self.tokens = tokenize.generate_tokens(readline)
self.index = 0
def consume_till(self, delim):
"""
consume tokens until colon
>>> tok = Tokenizer("for i in range(10): hello $i")
>>> tok.consume_till(":")
>>> tok.text[:tok.index]
'for i in range(10):'
>>> tok.text[tok.index:]
' hello $i'
"""
try:
while True:
t = next(self)
if t.value == delim:
break
elif t.value == "(":
self.consume_till(")")
elif t.value == "[":
self.consume_till("]")
elif t.value == "{":
self.consume_till("}")
# if end of line is found, it is an exception.
# Since there is no easy way to report the line number,
# leave the error reporting to the python parser later
# TODO this should be fixed
if t.value == "\n":
break
except:
# error_msg = "Expected {}, found end of line."
# raise ParseError(error_msg.format(repr(delim)))
# Raising ParseError doesn"t show the line number. If this error
# is ignored then it will be caught when compiling the python code
return
def __next__(self):
type, t, begin, end, line = next(self.tokens)
row, col = end
self.index = col
return Token(type=type, value=t, begin=begin, end=end)
