How to Mock Poetry pyproject.toml Dependencies Sections in Python

Parse and extract dependency lists from Poetry-style pyproject.toml text using Python's standard library.

Easy Python 3.9+ Aug 9, 2026 Modern tooling 15 views 0 copies

pyproject poetry toml dependencies parsing

Python code

59 lines

Python 3.9+

from pathlib import Path
import re


def parse_pyproject_dependencies(text):
    """Extract dependencies from a pyproject.toml style text."""
    lines = text.splitlines()
    sections = {
        "dependencies": [],
        "dev": [],
        "optional": [],
    }
    current_section = None

    patterns = {
        "dependencies": r"^dependencies\s*=\s*\[",
        "dev": r"^dev\s*=\s*\[",
        "optional": r"^optional-dependencies\s*=",
    }

    for idx, line in enumerate(lines):
        stripped = line.strip()
        for section, pattern in patterns.items():
            if re.match(pattern, line.strip()):
                current_section = section
                break

        if current_section and stripped.startswith('"') and stripped.endswith('",'):
            dependency = stripped.strip('",')
            sections[current_section].append(dependency)

        if current_section and stripped == "]":
            current_section = None

    return sections


if __name__ == "__main__":
    sample_pyproject = '''
[tool.poetry]
name = "demo"
version = "0.1.0"

[tool.poetry.dependencies]
python = "^3.9"
requests = "^2.31.0"
flask = "^3.0.0"

[tool.poetry.group.dev.dependencies]
pytest = "^7.4.0"
black = "^23.9.0"

[tool.poetry.extras]
speed = ["uvloop"]
'''

    result = parse_pyproject_dependencies(sample_pyproject)
    for section, deps in result.items():
        print(f"{section}: {deps}")

Output

stdout

dependencies: ['python', 'requests', 'flask']
dev: ['pytest', 'black']
optional: ['uvloop']

How it works

This parser reads a pyproject.toml string line-by-line, tracking the current TOML section with regex patterns for dependencies, dev, and optional-dependencies. It extracts lines that look like quoted strings inside dependency arrays, stripping quotes and commas. The parser resets the current section when it sees a closing bracket. This approach works for mocking or inspecting dependency structures without needing a TOML library, handy for quick checks, scripts, or test doubles.

Common mistakes

Not handling the closing bracket `]` correctly, which causes dependencies from later sections to leak into the previous section.
Assuming all dependency lines start with quotes — Poetry can use multiline arrays or unquoted package specs.
Forgetting to reset `current_section` when encountering a new `[tool.poetry...]` header, mixing groups incorrectly.

Variations

Use `tomllib` (Python 3.11+) to parse the file properly and access nested TOML tables.
Extend patterns to capture dependencies from `tool.poetry.group.*.dependencies` with multiple group names.

Real-world use cases

Emulating dependency extraction when testing a package manager CLI without installing Poetry.
Scanning a monorepo for Python dependency declarations during license or security audits.
Generating a quick inventory of required vs optional packages from a config file inside a CI script.

How to Mock Poetry pyproject.toml Dependencies Sections in Python

Python code

Output

How it works

Common mistakes

Variations

Real-world use cases

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Python code

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How it works

Common mistakes

Variations

Real-world use cases

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