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kirbylife
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# Python-generated files
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__pycache__/
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*.py[oc]
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build/
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dist/
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wheels/
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*.egg-info
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# Virtual environments
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.venv
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3.11
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DO WHAT THE FUCK YOU WANT TO PUBLIC LICENSE
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Version 2, December 2004
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Copyright (C) 2025 kirbylife <hola@kirbylife.dev>
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Everyone is permitted to copy and distribute verbatim or modified
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copies of this license document, and changing it is allowed as long
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as the name is changed.
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DO WHAT THE FUCK YOU WANT TO PUBLIC LICENSE
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TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION
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0. You just DO WHAT THE FUCK YOU WANT TO.
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# Jinja Low-Cost
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This is a toy template engine built using only what the Python standard library includes.
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It was created for three reasons:
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- Because at one of my jobs, I needed a dependency-free template engine.
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- As an experiment to see how far I could extend Python's default `Formatter`.
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- To write an article for [my blog](https://blog.kirbylife.dev/post/creando-un-motor-de-plantillas-ligero-y-malo-en-python-10).
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Inside `jinja_lowcost/main`, at the bottom of the file, you’ll find some usage examples—since I don’t plan to document it properly.
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This code is released under the **WTFPL 2.0** license, so feel free to use it however you like. But please, **do not use it in production**.
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from collections.abc import Callable
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from string import Formatter
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from typing import Any, Iterable
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from enum import Enum
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import re
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import shlex
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class Instruction(Enum):
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REPEAT = "repeat"
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JOIN = "join"
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IF = "if"
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LOWER = "lower"
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UPPER = "upper"
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STRIP = "strip"
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CALL = "call"
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NOP = "nop"
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class ConditionalOp(Enum):
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NOT = "not"
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EQUAL = "equal"
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NOTEQUAL = "notequal"
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EVEN = "even"
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ODD = "odd"
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CONTAINS = "contains"
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INSTRUCTION_PATTERN = re.compile("""(?!['|"].*):(?!.*['|"])""")
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class JinjaLowCost(Formatter):
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@staticmethod
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def parse_instruction(raw_instruction: str) -> tuple[Instruction, list[Any], str | None]:
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# Separar la instrucción con sus parámetros y la template
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binding = iter(re.split(INSTRUCTION_PATTERN, raw_instruction, maxsplit=1))
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pre_instruction = next(binding, None)
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# Sí no tiene ninguna instrucción, se retorna NOP
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if not pre_instruction:
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return Instruction.NOP, [], ""
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template = next(binding, None)
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# Separar la instrucción de sus parámetros respetando las comillas
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instruction, *params = shlex.split(pre_instruction)
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try:
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# Retornar todas las partes sí la instrucción está en el Enum
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return Instruction(instruction), params, template
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except ValueError:
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# Si no, retornar NOP
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return Instruction.NOP, [], ""
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def format_field(self, value: Any, format_spec: str) -> Any:
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instruction, params, template = self.parse_instruction(format_spec)
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match instruction:
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case Instruction.REPEAT:
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if isinstance(value, dict):
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elements = value.items()
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elif isinstance(value, int):
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elements = range(value)
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elif isinstance(value, Iterable):
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elements = value
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else:
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raise Exception(f"'{value}' is not iterable")
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if template is None:
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raise Exception("A template is needed")
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name = next(iter(params), "item")
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processed_elements = []
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for i, item in enumerate(elements):
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processed_element = self.format(template, **{name: item, "#": i})
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processed_elements.append(processed_element)
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return "".join(processed_elements)
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case Instruction.IF:
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if not params:
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return template if value else ""
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iter_params = iter(params)
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try:
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conditional = ConditionalOp(next(iter_params))
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except ValueError:
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raise Exception(f"'{params[0]}' is not a valid if conditional")
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criteria = next(iter_params, None)
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match conditional:
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case ConditionalOp.EQUAL:
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if criteria is None:
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raise Exception("Equal operator requires a parameter")
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func = lambda: value == type(value)(criteria)
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case ConditionalOp.NOTEQUAL:
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if criteria is None:
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raise Exception("NotEqual operator requires a parameter")
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func = lambda: value != type(value)(criteria)
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case ConditionalOp.CONTAINS:
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if criteria is None:
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raise Exception("Contains operator requires a parameter")
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func = lambda: value and type(value[0])(criteria) in value
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case ConditionalOp.EVEN:
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func = lambda: value % 2 == 0
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case ConditionalOp.ODD:
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func = lambda: value % 2 != 0
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case ConditionalOp.NOT:
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func = lambda: not value
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return template if func() else ""
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case Instruction.JOIN:
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if not isinstance(value, Iterable):
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raise Exception(f"{value} is not iterable")
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criteria = next(iter(params), "")
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return criteria.join(map(str, value))
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case Instruction.UPPER:
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return str(value).upper()
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case Instruction.LOWER:
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return str(value).lower()
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case Instruction.STRIP:
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param = next(iter(params), None)
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return str(value).strip(param)
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case Instruction.CALL:
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if not isinstance(value, Callable):
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raise Exception(f"{value} is not callable")
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return str(value(*params))
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case Instruction.NOP:
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try:
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return super().format_field(value, format_spec)
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except:
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raise Exception(f"Error trying to format '{format_spec}' instruction")
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f = JinjaLowCost()
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res = f.format("{x:join ', '}", x=[1, 2, 3, 4])
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print(res)
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res = f.format("{x:strip '-'}", x="----prueba----")
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print(res)
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# res = f.format("{a=}", a=10)
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# print(res)
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res = f.format("{x:repeat n:->{{n}}<-\n}", x=[10, 20, 30])
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print(res)
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res = f.format("{x:if contains {y}:estoy dentro}", x=[10, 20, 30], y=10)
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print(res)
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res = f.format("{x:if contains 42:42 is real}", x=range(10, 50))
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print(res)
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res = f.format("{x:join ', '}", x=[10, 20, 30])
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print(res)
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res = f.format("{x:upper}", x="Kirbylife")
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print(res)
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res = f.format("{x:lower}", x="TESTtestTEST")
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print(res)
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res = f.format("{x.get:call key_a}", x={"key_a": 10, "key_b": 20})
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print(res)
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res = f.format("{names:repeat name:{{#:if even:+ {{name}}\n}}{{#:if odd:- {{name:upper}}\n}}}", names=["Pastor", "Suadero", "Tripa"])
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print(res)
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template = "{numbers:repeat num:{{num}} }"
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print(f.format(template, numbers=[10, 20, 30]))
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res = f.format("{tacos: repeat taco:{{#}}. {{taco:upper}}\n}", tacos=["suadero", "pasTor", "tripa"])
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print(res)
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res = f.format(
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"{nums:repeat num:{{num: repeat n:{{{{n:02}}}} }}\n}",
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nums=[range(3), range(3,6), range(6, 9), range(9, 12)]
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)
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print(res)
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res = f.format("{n:repeat:{{#:repeat:* }}\n}", n=7)
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print(res)
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template = """
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<ul>{cities:repeat city:
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<li style="background-color: {{#:if even:gray}}{{#:if odd:lightgray}}">{{city}}</li>}
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</ul>
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"""
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print(f.format(template, cities=["New York", "New Delhi", "Tokio", "Monterrey"]))
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res = f.format("{name.title:call}", name="JiNjA LoW cOsT")
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print(res)
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res = f.format("{exchange.get:call {currency}} {currency}", exchange={"USD": 1, "MXN": 19.7}, currency="MXN")
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print(res)
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[project]
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name = "jinja-lowcost"
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version = "0.1.0"
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description = "proof-of-concept of a simple template engine written from scratch*"
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readme = "README.md"
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requires-python = ">=3.10"
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dependencies = []
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