Merge pull request #303 from realpython/first-match

How to Find the First Match Materials

Author: KateFinegan

python-first/README.md

@@ -0,0 +1,7 @@
+# How to Get the First Match From a Python List or Iterable
+
+The code samples and supporting materials for the [corresponding tutorial](https://realpython.com/python-first/) on Real Python.
+
+To run the chart scripts, you'll need to have `matplotlib` installed.
+
+Country data obtained from https://github.com/samayo/country-json

python-first/chart.py

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+"""
+Script to chart out the performance of generators and loops for finding the
+first matching element in a list.
+"""
+
+from timeit import timeit
+
+import matplotlib.pyplot as plt
+
+TIMEIT_TIMES = 1000  # Increase number for smoother lines
+LIST_SIZE = 500
+POSITION_INCREMENT = 10
+
+
+def build_list(size, fill, value, at_position):
+    return [value if i == at_position else fill for i in range(size)]
+
+
+def find_match_loop(iterable):
+    for value in iterable:
+        if value["population"] > 50:
+            return value
+
+
+def find_match_gen(iterable):
+    return next(value for value in iterable if value["population"] > 50)
+
+
+looping_times = []
+generator_times = []
+positions = []
+
+for position in range(0, LIST_SIZE, POSITION_INCREMENT):
+    print(
+        f"Progress {position / LIST_SIZE:.0%}",
+        end=f"{3 * ' '}\r",  # Clear previous characters and reset cursor
+    )
+
+    positions.append(position)
+
+    list_to_search = build_list(
+        size=LIST_SIZE,
+        fill={"country": "Nowhere", "population": 10},
+        value={"country": "Atlantis", "population": 100},
+        at_position=position,
+    )
+
+    looping_times.append(
+        timeit(
+            "find_match_loop(list_to_search)",
+            globals=globals(),
+            number=TIMEIT_TIMES,
+        )
+    )
+    generator_times.append(
+        timeit(
+            "find_match_gen(list_to_search)",
+            globals=globals(),
+            number=TIMEIT_TIMES,
+        )
+    )
+
+print("Progress 100%")
+
+fig, ax = plt.subplots()
+
+plot = ax.plot(positions, looping_times, label="loop")
+plot = ax.plot(positions, generator_times, label="generator")
+
+plt.xlim([0, LIST_SIZE])
+plt.ylim([0, max(max(looping_times), max(generator_times))])
+
+plt.xlabel("Index of element to be found")
+plt.ylabel(f"Time in seconds to find element {TIMEIT_TIMES:,} times")
+plt.title("Raw Time to Find First Match")
+plt.legend()
+
+plt.show()
+
+# Ratio
+
+looping_ratio = [loop / loop for loop in looping_times]
+generator_ratio = [
+    gen / loop for gen, loop in zip(generator_times, looping_times)
+]
+
+fig, ax = plt.subplots()
+
+plot = ax.plot(positions, looping_ratio, label="loop")
+plot = ax.plot(positions, generator_ratio, label="generator")
+
+plt.xlim([0, LIST_SIZE])
+plt.ylim([0, max(max(looping_ratio), max(generator_ratio))])
+
+plt.xlabel("Index of element to be found")
+plt.ylabel("Speed to find element, relative to loop")
+plt.title("Relative Speed to Find First Match")
+plt.legend()
+
+plt.show()

python-first/chart_gen_loop_in.py

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+"""
+Script to chart out the performance of generators, loops and the in operator
+when trying to find the first matching element in a list.
+"""
+
+from timeit import timeit
+
+import matplotlib.pyplot as plt
+
+TIMEIT_TIMES = 100  # Increase number for smoother lines
+LIST_SIZE = 1000
+POSITION_INCREMENT = 10
+
+looping_times = []
+generator_times = []
+in_times = []
+positions = []
+
+
+def build_list(size, fill, value, at_position):
+    return [value if i == at_position else fill for i in range(size)]
+
+
+def find_match_loop(list_to_search, item_to_find):
+    for value in list_to_search:
+        if value == item_to_find:
+            return value
+    return None
+
+
+def find_match_gen(list_to_search, item_to_find):
+    return next(
+        (value for value in list_to_search if value == item_to_find), None
+    )
+
+
+def find_match_in(list_to_search, item_to_find):
+    if item_to_find in list_to_search:
+        return item_to_find
+
+
+for position in range(0, LIST_SIZE, POSITION_INCREMENT):
+    print(
+        f"Progress {position / LIST_SIZE:.0%}",
+        end=f"{3 * ' '}\r",  # Clear previous characters and resets cursor
+    )
+
+    positions.append(position)
+
+    list_to_search = build_list(
+        LIST_SIZE, "Fake Python", "Real Python", position
+    )
+
+    looping_times.append(
+        timeit(
+            "find_match_loop(list_to_search, 'Real Python')",
+            globals=globals(),
+            number=TIMEIT_TIMES,
+        )
+    )
+    generator_times.append(
+        timeit(
+            "find_match_gen(list_to_search, 'Real Python')",
+            globals=globals(),
+            number=TIMEIT_TIMES,
+        )
+    )
+    in_times.append(
+        timeit(
+            "find_match_in(list_to_search, 'Real Python')",
+            globals=globals(),
+            number=TIMEIT_TIMES,
+        )
+    )
+
+print("Progress 100%")
+
+fig, ax = plt.subplots()
+
+plot = ax.plot(positions, looping_times, label="loop")
+plot = ax.plot(positions, generator_times, label="generator")
+plot = ax.plot(positions, in_times, label="in")
+
+plt.xlim([0, LIST_SIZE])
+plt.ylim([0, max(max(looping_times), max(generator_times), max(in_times))])
+
+plt.xlabel("Index of element to be found")
+plt.ylabel(f"Time in seconds to find element {TIMEIT_TIMES:,} times")
+plt.title("Raw Time to Find First Match")
+plt.legend()
+
+plt.show()
+
+# Ratio
+
+looping_ratio = [loop / loop for loop in looping_times]
+generator_ratio = [
+    gen / loop for gen, loop in zip(generator_times, looping_times)
+]
+in_ratio = [in_ / loop for in_, loop in zip(in_times, looping_times)]
+
+fig, ax = plt.subplots()
+
+plot = ax.plot(positions, looping_ratio, label="loop")
+plot = ax.plot(positions, generator_ratio, label="generator")
+plot = ax.plot(positions, in_ratio, label="in")
+
+plt.xlim([0, LIST_SIZE])
+plt.ylim([0, max(max(looping_ratio), max(generator_ratio), max(in_ratio))])
+plt.xlabel("Index of element to be found")
+plt.ylabel("Speed to find element, relative to loop")
+plt.title("Relative Speed to Find First Match")
+plt.legend()
+
+plt.show()