dep_graph.py

import os
import json
import sys
from json.decoder import JSONDecodeError


class CyclicalDependencyException(Exception):
    """Exception raised when a cyclical dependency is detected"""
    pass


class DependencyGraph:
    """Class to consume and traverse a package list from json format."""

    def __init__(self, json_filepath):
        self.graph = self.read_json(json_filepath)

    @staticmethod
    def read_json(json_filepath):
        """consume a json file and return it as an adjacency list
        Args:
            json_filepath (str): filepath of the json to consume
        Returns:
            adj_list (dict): the json as an adjacency list
            """
        if not os.path.exists(json_filepath):
            raise FileNotFoundError(f'JSON file {json_filepath} '
                                    f'does not exist on this system.')
        try:
            with open(json_filepath) as json_file:
                adj_list = json.load(json_file)
        except JSONDecodeError:
            raise TypeError(f'File {json_filepath} is not in the correct '
                            f'json format.')
        return adj_list

    def print_graph(self):
        """Prints the graph in fully-traversed bulletpoint format"""
        for package in list(self.graph.keys()):
            self.traverse_dependencies(package)

    def traverse_dependencies(self, package, indent=0, visited=None):
        """Recursive method to traverse all dependencies.
        Args:
            package (str): package to traverse sub-dependencies of
            indent (int): number of indents to print with the current package
            visited (set): set of nodes that have been visited
            """
        if visited is None:
            visited = set()
        if package in visited:
            raise CyclicalDependencyException('CYCLICAL DEPENDENCY DETECTED')
        print(" " * indent + f"- {package}")
        visited.add(package)
        if package in self.graph:
            dependency_list = self.graph[package]
            for item in dependency_list:
                self.traverse_dependencies(item, indent+2, visited)
                visited.remove(item)


if __name__ == '__main__':
    if len(sys.argv) >= 2:
        # allow the user to provide the target json from the command line.
        # we check the second arg, since the first one is this script.
        target_json = sys.argv[1]
    else:
        target_json = 'test_files/example.json'  # default to example file
    d = DependencyGraph(target_json)
    d.print_graph()