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itertools-in-python3/README.md

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+# Itertools In Python 3, By Example
+
+> Supplemental materials for the [Itertools In Python 3, By Example](https://realpython.com/itertools-in-python3) article on [Real Python](https://realpython.com).

itertools-in-python3/sp500.py

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+from collections import namedtuple
+import csv
+from datetime import datetime
+import itertools as it
+import functools as ft
+
+
+class DataPoint(namedtuple('DataPoint', ['date', 'value'])):
+    __slots__ = ()
+
+    def __le__(self, other):
+        return self.value <= other.value
+
+    def __lt__(self, other):
+        return self.value < other.value
+
+    def __gt__(self, other):
+        return self.value > other.value
+
+
+def consecutive_positives(sequence, zero=0):
+    def _consecutives():
+        for itr in it.repeat(iter(sequence)):
+            yield tuple(it.takewhile(lambda p: p > zero,
+                                     it.dropwhile(lambda p: p <= zero, itr)))
+    return it.takewhile(lambda t: len(t), _consecutives())
+
+
+def read_prices(csvfile, _strptime=datetime.strptime):
+    with open(csvfile) as infile:
+        reader = csv.DictReader(infile)
+        for row in reader:
+            yield DataPoint(date=_strptime(row['Date'], '%Y-%m-%d').date(),
+                            value=float(row['Adj Close']))
+
+
+# Read prices and calculate daily percent change.
+prices = tuple(read_prices('SP500.csv'))
+gains = tuple(DataPoint(day.date, 100*(day.value/prev_day.value - 1.))
+              for day, prev_day in zip(prices[1:], prices))
+
+# Find maximum daily gain/loss.
+zdp = DataPoint(None, 0)  # zero DataPoint
+max_gain = ft.reduce(max, it.filterfalse(lambda p: p <= zdp, gains))
+max_loss = ft.reduce(min, it.filterfalse(lambda p: p > zdp, gains), zdp)
+
+
+# Find longest growth streak.
+growth_streaks = consecutive_positives(gains, zero=DataPoint(None, 0))
+longest_streak = ft.reduce(lambda x, y: x if len(x) > len(y) else y,
+                           growth_streaks)
+
+# Display results.
+print('Max gain: {1:.2f}% on {0}'.format(*max_gain))
+print('Max loss: {1:.2f}% on {0}'.format(*max_loss))
+
+print('Longest growth streak: {num_days} days ({first} to {last})'.format(
+    num_days=len(longest_streak),
+    first=longest_streak[0].date,
+    last=longest_streak[-1].date
+))