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The Terragrunt Guide Creates the Problem It Solves

Gruntwork’s “Terralith to Terragrunt” guide is well-written and comprehensive. It’s also a masterclass in manufacturing complexity to sell a solution.

I walked through the guide step by step. Here’s where it goes wrong — and what to do instead.

Step 1: A Reasonable Start

You begin with flat resources in a live/ directory. S3 bucket, DynamoDB table, IAM role, Lambda function. All in one state file. Simple.

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#!/usr/bin/env python3
# /// script
# dependencies = [
#     "flask",
#     "requests",
#     "pyjwt[crypto]",
#     "cryptography"
# ]
# ///

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Project Guidelines

Favor Class Composition Over Inheritance

• Reduced Coupling: Using composition over inheritance reduces coupling between classes, making the codebase easier to maintain and understand.
• Explicit Dependencies: It's clear what dependencies are required by a class.
• Increased Flexibility: Composition allows dynamic behavior swapping, unlike inheritance which is static.
• Ease of Testing: Testing composed objects is often simpler because you can isolate components.

# Good: Using Composition

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"""
Calculates test coverage for the new code only, that is for the added and
changed lines of code.

Usage:

pytest --cov --cov-report=xml
git diff master..HEAD |python calculate_new_coverage.py --coverage-report coverage.xml
"""

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import inspect
from argparse import ArgumentParser


def argparse_call(fn):
    sig = inspect.signature(fn)
    p = ArgumentParser()
    for param in sig.parameters.values():
        kwargs = {
            'type': param.annotation,

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from functools import wraps
from typing import TypedDict

from pydantic import BaseModel, validate_arguments


def replace_typed_dict_annotations(annotations):
    new_annotations = {}
    for k, T in annotations.items():
        if type(T).__name__ == '_TypedDictMeta':

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from typing import (
    Any,
    Dict,
    NamedTuple,
)

import pytest


class Case(NamedTuple):

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from dataclasses import dataclass

import pytest

from lib.util import paths_eq


from collections.abc import Mapping

_MISS = object()

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from functools import partial


class F:
    __slots__ = ('fns',)
    
    def __init__(self, *fns):
        self.fns = fns

    def __call__(self, *args, **kwargs):

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class compose:
    __slots__ = ('f', 'fs')
    
    def __init__(self, *fs):
        self.f, *self.fs = reversed(fs)

    def __call__(self, *args, **kwargs):
        result = self.f(*args, **kwargs)
        for f in self.fs:
            result = f(result)