ch05

Author: adii1823

ch05/decorate.sort.undecorate.py

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+# decorate.sort.undecorate.py
+from pprint import pprint
+
+
+students = [
+    dict(id=0, credits=dict(math=9, physics=6, history=7)),
+    dict(id=1, credits=dict(math=6, physics=7, latin=10)),
+    dict(id=2, credits=dict(history=8, physics=9, chemistry=10)),
+    dict(id=3, credits=dict(math=5, physics=5, geography=7)),
+]
+
+
+def decorate(student):
+    # create a 2-tuple (sum of credits, student) from student dict
+    return (sum(student['credits'].values()), student)
+pprint(decorate(students[0]))
+
+
+def undecorate(decorated_student):
+    # discard sum of credits, return original student dict
+    return decorated_student[1]
+
+
+students = sorted(map(decorate, students), reverse=True)
+students = list(map(undecorate, students))
+pprint(students)

ch05/dictionary.comprehensions.duplicates.py

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+# dictionary.comprehensions.duplicates.py
+word = 'Hello'
+
+swaps = {c: c.swapcase() for c in word}
+
+print(swaps)  # prints: {'H': 'h', 'e': 'E', 'l': 'L', 'o': 'O'}

ch05/dictionary.comprehensions.positions.py

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+# dictionary.comprehensions.positions.py
+word = 'Hello'
+
+positions = {c: k for k, c in enumerate(word)}
+
+print(positions)  # prints: {'H': 0, 'e': 1, 'l': 3, 'o': 4}

ch05/dictionary.comprehensions.py

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+# dictionary.comprehensions.py
+from string import ascii_lowercase
+
+
+lettermap = {c: k for k, c in enumerate(ascii_lowercase, 1)}
+# lettermap = dict((c, k) for k, c in enumerate(ascii_lowercase, 1))
+
+
+from pprint import pprint
+pprint(lettermap)

ch05/even.squares.py

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+# even.squares.py
+# using map and filter
+sq1 = list(
+    map(lambda n: n ** 2, filter(lambda n: not n % 2, range(10)))
+)
+
+# equivalent, but using list comprehensions
+sq2 = [n ** 2 for n in range(10) if not n % 2]
+
+print(sq1, sq1 == sq2)  # prints: [0, 4, 16, 36, 64] True

ch05/fibonacci.elegant.py

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+# fibonacci.elegant.py
+def fibonacci(N):
+    """Return all fibonacci numbers up to N. """
+    a, b = 0, 1
+    while a <= N:
+        yield a
+        a, b = b, a + b
+
+
+print(list(fibonacci(0)))   # [0]
+print(list(fibonacci(1)))   # [0, 1, 1]
+print(list(fibonacci(50)))  # [0, 1, 1, 2, 3, 5, 8, 13, 21, 34]

ch05/fibonacci.first.py

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+# fibonacci.first.py
+def fibonacci(N):
+    """Return all fibonacci numbers up to N. """
+    result = [0]
+    next_n = 1
+    while next_n <= N:
+        result.append(next_n)
+        next_n = sum(result[-2:])
+    return result
+
+
+print(fibonacci(0))   # [0]
+print(fibonacci(1))   # [0, 1, 1]
+print(fibonacci(50))  # [0, 1, 1, 2, 3, 5, 8, 13, 21, 34]

ch05/fibonacci.second.py

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+# fibonacci.second.py
+def fibonacci(N):
+    """Return all fibonacci numbers up to N. """
+    yield 0
+    if N == 0:
+        return
+    a = 0
+    b = 1
+    while b <= N:
+        yield b
+        a, b = b, a + b
+
+
+print(list(fibonacci(0)))   # [0]
+print(list(fibonacci(1)))   # [0, 1, 1]
+print(list(fibonacci(50)))  # [0, 1, 1, 2, 3, 5, 8, 13, 21, 34]

ch05/filter.py

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+# filter.py
+# This is not a valid Python module - Don't run it.
+
+>>> test = [2, 5, 8, 0, 0, 1, 0]
+>>> list(filter(None, test))
+[2, 5, 8, 1]
+>>> list(filter(lambda x: x, test))  # equivalent to previous one
+[2, 5, 8, 1]
+>>> list(filter(lambda x: x > 4, test))  # keep only items > 4
+[5, 8]

ch05/first.n.squares.manual.method.py

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+# first.n.squares.manual.method.py
+def get_squares_gen(n):
+    for x in range(n):
+        yield x ** 2
+
+squares = get_squares_gen(3)
+print(squares.__next__())  # prints: 0
+print(squares.__next__())  # prints: 1
+print(squares.__next__())  # prints: 4
+# the following raises StopIteration, the generator is exhausted,
+# any further call to next will keep raising StopIteration
+print(squares.__next__())