309 lines
11 KiB
Python
309 lines
11 KiB
Python
# Licensed under the Apache License: http://www.apache.org/licenses/LICENSE-2.0
|
|
# For details: https://github.com/nedbat/coveragepy/blob/master/NOTICE.txt
|
|
|
|
"""A simple Python template renderer, for a nano-subset of Django syntax.
|
|
|
|
For a detailed discussion of this code, see this chapter from 500 Lines:
|
|
http://aosabook.org/en/500L/a-template-engine.html
|
|
|
|
"""
|
|
|
|
# Coincidentally named the same as http://code.activestate.com/recipes/496702/
|
|
|
|
from __future__ import annotations
|
|
|
|
import re
|
|
|
|
from typing import (
|
|
Any, Callable, Dict, List, NoReturn, Optional, Set, Union, cast,
|
|
)
|
|
|
|
|
|
class TempliteSyntaxError(ValueError):
|
|
"""Raised when a template has a syntax error."""
|
|
pass
|
|
|
|
|
|
class TempliteValueError(ValueError):
|
|
"""Raised when an expression won't evaluate in a template."""
|
|
pass
|
|
|
|
|
|
class CodeBuilder:
|
|
"""Build source code conveniently."""
|
|
|
|
def __init__(self, indent: int = 0) -> None:
|
|
self.code: List[Union[str, CodeBuilder]] = []
|
|
self.indent_level = indent
|
|
|
|
def __str__(self) -> str:
|
|
return "".join(str(c) for c in self.code)
|
|
|
|
def add_line(self, line: str) -> None:
|
|
"""Add a line of source to the code.
|
|
|
|
Indentation and newline will be added for you, don't provide them.
|
|
|
|
"""
|
|
self.code.extend([" " * self.indent_level, line, "\n"])
|
|
|
|
def add_section(self) -> CodeBuilder:
|
|
"""Add a section, a sub-CodeBuilder."""
|
|
section = CodeBuilder(self.indent_level)
|
|
self.code.append(section)
|
|
return section
|
|
|
|
INDENT_STEP = 4 # PEP8 says so!
|
|
|
|
def indent(self) -> None:
|
|
"""Increase the current indent for following lines."""
|
|
self.indent_level += self.INDENT_STEP
|
|
|
|
def dedent(self) -> None:
|
|
"""Decrease the current indent for following lines."""
|
|
self.indent_level -= self.INDENT_STEP
|
|
|
|
def get_globals(self) -> Dict[str, Any]:
|
|
"""Execute the code, and return a dict of globals it defines."""
|
|
# A check that the caller really finished all the blocks they started.
|
|
assert self.indent_level == 0
|
|
# Get the Python source as a single string.
|
|
python_source = str(self)
|
|
# Execute the source, defining globals, and return them.
|
|
global_namespace: Dict[str, Any] = {}
|
|
exec(python_source, global_namespace)
|
|
return global_namespace
|
|
|
|
|
|
class Templite:
|
|
"""A simple template renderer, for a nano-subset of Django syntax.
|
|
|
|
Supported constructs are extended variable access::
|
|
|
|
{{var.modifier.modifier|filter|filter}}
|
|
|
|
loops::
|
|
|
|
{% for var in list %}...{% endfor %}
|
|
|
|
and ifs::
|
|
|
|
{% if var %}...{% endif %}
|
|
|
|
Comments are within curly-hash markers::
|
|
|
|
{# This will be ignored #}
|
|
|
|
Lines between `{% joined %}` and `{% endjoined %}` will have lines stripped
|
|
and joined. Be careful, this could join words together!
|
|
|
|
Any of these constructs can have a hyphen at the end (`-}}`, `-%}`, `-#}`),
|
|
which will collapse the white space following the tag.
|
|
|
|
Construct a Templite with the template text, then use `render` against a
|
|
dictionary context to create a finished string::
|
|
|
|
templite = Templite('''
|
|
<h1>Hello {{name|upper}}!</h1>
|
|
{% for topic in topics %}
|
|
<p>You are interested in {{topic}}.</p>
|
|
{% endif %}
|
|
''',
|
|
{"upper": str.upper},
|
|
)
|
|
text = templite.render({
|
|
"name": "Ned",
|
|
"topics": ["Python", "Geometry", "Juggling"],
|
|
})
|
|
|
|
"""
|
|
def __init__(self, text: str, *contexts: Dict[str, Any]) -> None:
|
|
"""Construct a Templite with the given `text`.
|
|
|
|
`contexts` are dictionaries of values to use for future renderings.
|
|
These are good for filters and global values.
|
|
|
|
"""
|
|
self.context = {}
|
|
for context in contexts:
|
|
self.context.update(context)
|
|
|
|
self.all_vars: Set[str] = set()
|
|
self.loop_vars: Set[str] = set()
|
|
|
|
# We construct a function in source form, then compile it and hold onto
|
|
# it, and execute it to render the template.
|
|
code = CodeBuilder()
|
|
|
|
code.add_line("def render_function(context, do_dots):")
|
|
code.indent()
|
|
vars_code = code.add_section()
|
|
code.add_line("result = []")
|
|
code.add_line("append_result = result.append")
|
|
code.add_line("extend_result = result.extend")
|
|
code.add_line("to_str = str")
|
|
|
|
buffered: List[str] = []
|
|
|
|
def flush_output() -> None:
|
|
"""Force `buffered` to the code builder."""
|
|
if len(buffered) == 1:
|
|
code.add_line("append_result(%s)" % buffered[0])
|
|
elif len(buffered) > 1:
|
|
code.add_line("extend_result([%s])" % ", ".join(buffered))
|
|
del buffered[:]
|
|
|
|
ops_stack = []
|
|
|
|
# Split the text to form a list of tokens.
|
|
tokens = re.split(r"(?s)({{.*?}}|{%.*?%}|{#.*?#})", text)
|
|
|
|
squash = in_joined = False
|
|
|
|
for token in tokens:
|
|
if token.startswith("{"):
|
|
start, end = 2, -2
|
|
squash = (token[-3] == "-")
|
|
if squash:
|
|
end = -3
|
|
|
|
if token.startswith("{#"):
|
|
# Comment: ignore it and move on.
|
|
continue
|
|
elif token.startswith("{{"):
|
|
# An expression to evaluate.
|
|
expr = self._expr_code(token[start:end].strip())
|
|
buffered.append("to_str(%s)" % expr)
|
|
else:
|
|
# token.startswith("{%")
|
|
# Action tag: split into words and parse further.
|
|
flush_output()
|
|
|
|
words = token[start:end].strip().split()
|
|
if words[0] == "if":
|
|
# An if statement: evaluate the expression to determine if.
|
|
if len(words) != 2:
|
|
self._syntax_error("Don't understand if", token)
|
|
ops_stack.append("if")
|
|
code.add_line("if %s:" % self._expr_code(words[1]))
|
|
code.indent()
|
|
elif words[0] == "for":
|
|
# A loop: iterate over expression result.
|
|
if len(words) != 4 or words[2] != "in":
|
|
self._syntax_error("Don't understand for", token)
|
|
ops_stack.append("for")
|
|
self._variable(words[1], self.loop_vars)
|
|
code.add_line(
|
|
"for c_{} in {}:".format(
|
|
words[1],
|
|
self._expr_code(words[3])
|
|
)
|
|
)
|
|
code.indent()
|
|
elif words[0] == "joined":
|
|
ops_stack.append("joined")
|
|
in_joined = True
|
|
elif words[0].startswith("end"):
|
|
# Endsomething. Pop the ops stack.
|
|
if len(words) != 1:
|
|
self._syntax_error("Don't understand end", token)
|
|
end_what = words[0][3:]
|
|
if not ops_stack:
|
|
self._syntax_error("Too many ends", token)
|
|
start_what = ops_stack.pop()
|
|
if start_what != end_what:
|
|
self._syntax_error("Mismatched end tag", end_what)
|
|
if end_what == "joined":
|
|
in_joined = False
|
|
else:
|
|
code.dedent()
|
|
else:
|
|
self._syntax_error("Don't understand tag", words[0])
|
|
else:
|
|
# Literal content. If it isn't empty, output it.
|
|
if in_joined:
|
|
token = re.sub(r"\s*\n\s*", "", token.strip())
|
|
elif squash:
|
|
token = token.lstrip()
|
|
if token:
|
|
buffered.append(repr(token))
|
|
|
|
if ops_stack:
|
|
self._syntax_error("Unmatched action tag", ops_stack[-1])
|
|
|
|
flush_output()
|
|
|
|
for var_name in self.all_vars - self.loop_vars:
|
|
vars_code.add_line(f"c_{var_name} = context[{var_name!r}]")
|
|
|
|
code.add_line("return ''.join(result)")
|
|
code.dedent()
|
|
self._render_function = cast(
|
|
Callable[
|
|
[Dict[str, Any], Callable[..., Any]],
|
|
str
|
|
],
|
|
code.get_globals()["render_function"],
|
|
)
|
|
|
|
def _expr_code(self, expr: str) -> str:
|
|
"""Generate a Python expression for `expr`."""
|
|
if "|" in expr:
|
|
pipes = expr.split("|")
|
|
code = self._expr_code(pipes[0])
|
|
for func in pipes[1:]:
|
|
self._variable(func, self.all_vars)
|
|
code = f"c_{func}({code})"
|
|
elif "." in expr:
|
|
dots = expr.split(".")
|
|
code = self._expr_code(dots[0])
|
|
args = ", ".join(repr(d) for d in dots[1:])
|
|
code = f"do_dots({code}, {args})"
|
|
else:
|
|
self._variable(expr, self.all_vars)
|
|
code = "c_%s" % expr
|
|
return code
|
|
|
|
def _syntax_error(self, msg: str, thing: Any) -> NoReturn:
|
|
"""Raise a syntax error using `msg`, and showing `thing`."""
|
|
raise TempliteSyntaxError(f"{msg}: {thing!r}")
|
|
|
|
def _variable(self, name: str, vars_set: Set[str]) -> None:
|
|
"""Track that `name` is used as a variable.
|
|
|
|
Adds the name to `vars_set`, a set of variable names.
|
|
|
|
Raises an syntax error if `name` is not a valid name.
|
|
|
|
"""
|
|
if not re.match(r"[_a-zA-Z][_a-zA-Z0-9]*$", name):
|
|
self._syntax_error("Not a valid name", name)
|
|
vars_set.add(name)
|
|
|
|
def render(self, context: Optional[Dict[str, Any]] = None) -> str:
|
|
"""Render this template by applying it to `context`.
|
|
|
|
`context` is a dictionary of values to use in this rendering.
|
|
|
|
"""
|
|
# Make the complete context we'll use.
|
|
render_context = dict(self.context)
|
|
if context:
|
|
render_context.update(context)
|
|
return self._render_function(render_context, self._do_dots)
|
|
|
|
def _do_dots(self, value: Any, *dots: str) -> Any:
|
|
"""Evaluate dotted expressions at run-time."""
|
|
for dot in dots:
|
|
try:
|
|
value = getattr(value, dot)
|
|
except AttributeError:
|
|
try:
|
|
value = value[dot]
|
|
except (TypeError, KeyError) as exc:
|
|
raise TempliteValueError(
|
|
f"Couldn't evaluate {value!r}.{dot}"
|
|
) from exc
|
|
if callable(value):
|
|
value = value()
|
|
return value
|