Example MovieCatalog code to refactor

README.md

Before and After Refactoring of MovieCatalog

1. blah blah
2. blah blah

movie_catalog.py

from movie import Movie

class MovieCatalog:
    """A movie catalog."""                      # 7. Communicate in Code

    def __init__(self):
        self.catalog = []                       # 6. Divide Long Method
        with open('movies.csv', 'r') as file:   # 1. Rename
            rows = csv.reader(file)             # 1. Rename, 5. Fix Latent Error
            for r in rows:                      # 1. Rename
                if not r:
                    continue
                if not r[0].startswith('#'):    # 2. Replace Nested if with Guard
                    try:
                        self.catalog.append(
                            Movie(r[1],r[2],r[3].split('|'))) # 4. Intro Var
                    except IndexError:          # 3. Replace Exception with Test
                        logging.error(
                        f'Line {rows.line_num}:\
                        Unrecognized format "{",".join(r)}"')
    
    
    def get_movie(self, movie_name, year: int = None):
        """Get a movie from the catalog that matches the parameter values."""
        all_match: Dict[int,Movie] = {}
        for movie in self.catalog:
            if year is not None:
                if year == movie.year and movie.get_title() == movie_name:
                    return movie
            else:
                if movie.get_title() == movie_name:
                    all_match[movie.year] = movie
        if all_match:
            return all_match[max(all_match)]

movie_catalog_refactored.py

# After Refactoring
import csv
import logging
from movie import Movie
from typing import Dict

MOVIE_DATA_FILE = 'movies.csv'

class MovieCatalog:
    """Searchable collection of Movies, using data from a file."""
    
    def __init__(self):
        self.catalog = self.load_movie_catalog(MOVIE_DATA_FILE)

    def load_movie_catalog(self, data_file):
        """Read CSV data from a file and create movies."""
        catalog = []
        with open(data_file, 'r') as csv_file:
            csv_data = csv.reader(csv_file, skipinitialspace=True)
            for movie_data in csv_data:
                # the CSV data may contain blank lines and comment (#) lines
                if not movie_data or movie_data[0].startswith('#'):
                    continue
                if len(movie_data) != 4:
                    logging.error(
                        f'Line {csv_data.line_num}: Unrecognized format "{",".join(movie_data)}"')
                    continue
                (_, title, year, genre_string) = movie_data
                catalog.append(Movie(title, year, genre_string.split('|')))
 
        return catalog
                    

    def get_movie(self, title, year = None):
        """Get a movie from the catalog that matches the parameter values."""
        # 1. avoid repeated "if year is not None" inside of long for loop
        # 2. replace for loop with list comprehension
        # Movies are in reverse chronological order, so if the year
        # is not specified then return the first match by title

        if year is None:
            # match by title only
            matches = lambda movie : movie.title == title
        else:
            # match by title and year released
            matches = lambda movie: movie.title == title and movie.year == year
        try:
            # use next() for short-circuit evaluation. Returns first match.
            return next(movie for movie in self.catalog if matches(movie))
        except StopIteration:
            # no match
            return None