Merge pull request #519 from realpython/python-lazy-evaluation

python-lazy-evaluation

Author: brendaweles

python-lazy-evaluation/README.md

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+# What's Lazy Evaluation in Python?
+
+A summary of the code used in the [What's Lazy Evaluation in Python?](https://realpython.com/python-lazy-evaluation/) tutorial on Real Python.

python-lazy-evaluation/exploring_itertools_chain.py

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+"""
+Exploring the itertools module
+"""
+
+import itertools
+import sys
+
+# Explore itertools.chain()
+first_team = ["Sarah", "Matt", "Jim", "Denise", "Kate"]
+second_team = ["Mark", "Zara", "Mo", "Jennifer", "Owen"]
+
+for name in itertools.chain(first_team, second_team):
+    print(name)
+
+# Verify changes in reference counts
+print(sys.getrefcount(first_team))
+
+quiz_team = itertools.chain(first_team, second_team)
+print(sys.getrefcount(first_team))
+
+for name in quiz_team:
+    print(name)
+
+print(sys.getrefcount(first_team))

python-lazy-evaluation/exploring_itertools_islice.py

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+"""
+Exploring the itertools module
+"""
+
+import itertools
+
+numbers = [2, 4, 6, 8, 10]
+standard_slice = numbers[1:4]
+iterator_slice = itertools.islice(numbers, 1, 4)
+
+# Change third element in numbers
+numbers[2] = 999
+
+print(numbers)
+
+print("\nStandard slice:")
+for number in standard_slice:
+    print(number)
+
+print("\nIterator slice:")
+for number in iterator_slice:
+    print(number)

python-lazy-evaluation/generator_expressions.py

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+"""
+Exploring generator expressions
+"""
+
+import random
+
+# List comprehension
+coin_toss = ["Heads" if random.random() > 0.5 else "Tails" for _ in range(10)]
+
+print(f"List comprehension:\n{coin_toss}")
+
+# Generator expression
+coin_toss = ("Heads" if random.random() > 0.5 else "Tails" for _ in range(10))
+print(f"\nGenerator expression:\n{coin_toss}")
+
+print(f"\nFirst coin toss: {next(coin_toss)}")
+print(f"Second coin toss: {next(coin_toss)}")
+
+# Print remaining coin tosses
+for toss_result in coin_toss:
+    print(toss_result)
+
+# Defining a generator function
+
+
+def generate_coin_toss(number):
+    for _ in range(number):
+        yield "Heads" if random.random() > 0.5 else "Tails"
+
+
+coin_toss = generate_coin_toss(10)
+print("\nUsing a generator function:")
+print(next(coin_toss))
+print(next(coin_toss))
+
+for toss_result in coin_toss:
+    print(toss_result)

python-lazy-evaluation/infinite_elements.py

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+"""
+Creating an infinite sequence of elements using generators
+"""
+
+import itertools
+
+quarters = itertools.count(start=0, step=0.25)
+# Print the first 8 elements, however, the sequence is infinite
+for _ in range(8):
+    print(next(quarters))
+
+names = ["Sarah", "Matt", "Jim", "Denise", "Kate"]
+rota = itertools.cycle(names)
+print(rota)
+
+print(next(rota))
+print(next(rota))
+print(next(rota))
+
+
+# Use a generator function
+def generate_rota(iterable):
+    index = 0
+    length = len(iterable)
+    while True:
+        yield iterable[index]
+        if index == length - 1:
+            index = 0
+        else:
+            index += 1
+
+
+rota = generate_rota(names)
+print("\nUsing a generator function")
+for _ in range(12):
+    print(next(rota))

python-lazy-evaluation/reading_csv_file.py

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+"""
+Eager and lazy options for reading a CSV file
+"""
+
+import csv
+import pprint
+
+print("Eager evaluation using 'open()'")
+with open("superhero_pets.csv", encoding="utf-8") as file:
+    data = file.readlines()
+
+pprint.pprint(data)
+
+print("\nLazy evaluation using 'csv.reader()'")
+with open("superhero_pets.csv", encoding="utf-8", newline="") as file:
+    data = csv.reader(file)
+    print(data)
+
+    print(next(data))
+    print(next(data))
+    print(next(data))
+
+    for row in data:
+        print(row)

python-lazy-evaluation/superhero_pets.csv

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+Pet Name,Species,Superpower,Favorite Snack,Hero Owner
+Whiskertron,Cat,Teleportation,Tuna,Catwoman
+Flashpaw,Dog,Super Speed,Peanut Butter,The Flash
+Mystique,Squirrel,Illusion,Nuts,Doctor Strange
+Quackstorm,Duck,Weather Control,Bread crumbs,Storm
+Bark Knight,Dog,Darkness Manipulation,Bacon,Batman

python-lazy-evaluation/using_enumerate.py

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+"""
+Exploring 'enumerate()' lazy evaluation
+"""
+
+import random
+
+names = ["Sarah", "Matt", "Jim", "Denise", "Kate"]
+random.shuffle(names)
+print(names)
+
+# Using `enumerate()` in a 'for' loop
+for index, name in enumerate(names, start=1):
+    print(f"{index}. {name}")
+
+# Using `enumerate()` with 'next()'
+numbered_names = enumerate(names, start=1)
+print(numbered_names)
+
+print(next(numbered_names))
+print(next(numbered_names))
+
+# Update third name
+names[2] = "The Coffee Robot"
+print(next(numbered_names))
+# Output: (3, 'The Coffee Robot')

python-lazy-evaluation/using_map_and_filter.py

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+"""
+Exploring 'map()' and 'filter()'
+"""
+
+original_names = ["Sarah", "Matt", "Jim", "Denise", "Kate", "Andy"]
+names = filter(lambda x: ("a" in x) or ("A" in x), original_names)
+names = filter(lambda x: len(x) == 4, names)
+names = map(str.upper, names)
+
+print(list(names))

python-lazy-evaluation/using_zip.py

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+"""
+Exploring 'zip()' lazy evaluation
+"""
+
+import random
+
+names = ["Sarah", "Matt", "Jim", "Denise", "Kate"]
+weekdays = ["Monday", "Tuesday", "Wednesday", "Thursday", "Friday"]
+random.shuffle(names)
+print(names)
+
+# Using 'zip()' in a 'for' loop
+for day, name in zip(weekdays, names):
+    print(f"{day}: {name}")
+
+# Using 'zip()' with 'next()'
+day_name_pairs = zip(weekdays, names)
+print(next(day_name_pairs))
+print(next(day_name_pairs))
+
+# Update third name
+names[2] = "The Coffee Robot"
+print(next(day_name_pairs))
+# Output: ('Wednesday', 'The Coffee Robot')