はじめに
Pythonエンジニア認定試験に興味をもったので、
Pythonチュートリアル（第4版）をひたすら写経していきたくなったので、
写経したいと思います。（コード部分のみ）
ただし、プロンプト表記のところは全部pyファイル化して書きなおします。
今回は4章部分のみです。
4章 制御構造ツール
4.1 if文
x = int(input("整数を入れてください:"))
# 整数を入れてください:42
# もっと
if x < 0:
x = 0
print('負数はゼロとする')
elif x == 0:
print('ゼロ')
elif x == 1:
print('1つ')
else:
print('もっと')
4.2 for文
words = ['cat', 'window', 'defenestrate']
# cat 3
# window 6
# defenestrate 12
for w in words:
print(w,len(w))
users = {'taro': 'inactive', 'jiro': 'active', 'saburo': 'inactive'}
for user, status in users.copy().items():
if status == 'inactive':
del users[user]
# {'jiro': 'active'}
print(users)
#初期化
users = {'taro': 'inactive', 'jiro': 'active', 'saburo': 'inactive'}
active_users = {}
for user, status in users.items():
if status == 'active':
active_users[user] = status
# {'jiro': 'active'}
print(active_users)
4.3 range()関数
# 0 1 2 3 4
for i in range(5):
print(i, end=' ')
print()
# 5 6 7 8 9
for i in range(5, 10):
print(i, end=' ')
print()
# 0 3 6 9
for i in range(0, 10, 3):
print(i, end=' ')
print()
# -10 -40 -70
for i in range(-10,-100,-30):
print(i, end=' ')
print()
a = ['Mary', 'had', 'a', 'little', 'lamb']
# 0 Mary
# 1 had
# 2 a
# 3 little
# 4 lamb
for i in range(len(a)):
print(i, a[i])
# range(0, 10)
print(range(10))
# 6
print(sum(range(4))) # 0 + 1 + 2 + 3
# [0, 1, 2, 3]
print(list(range(4)))
4.4 break文とcontinue文、ループにおけるelse節
# 2 is a prime number
# 3 is a prime number
# 4 ezuals 2 * 2
# 5 is a prime number
# 6 ezuals 2 * 3
# 7 is a prime number
# 8 ezuals 2 * 4
# 9 ezuals 3 * 3
for n in range(2, 10):
for x in range(2, n):
if n % x == 0:
print(n, 'ezuals', x, '*', n//x)
break
else:
# ループで約数を見つけられなかった場合
print(n, 'is a prime number')
# Found an even number 2
# Found an odd number 3
# Found an even number 4
# Found an odd number 5
# Found an even number 6
# Found an odd number 7
# Found an even number 8
# Found an odd number 9
for num in range(2, 10):
if num % 2 == 0:
print("Found an even number", num)
continue
print("Found an odd number", num)
4.5 pass文
while True:
pass # ビジーウェイトでキーボード割り込み(Ctrl+C)をまつ
print("test") # 実行されない
# class MyEmptyClass:
# pass
def intlog(*args):
pass # 実装を忘れないこと！
4.6 関数の定義
def fib(n):
"""nまでのフィボナッチ級数を表示する"""
a , b= 0, 1
while a < n:
print(a, end= ' ')
a, b = b, a+b
print()
# ではこの関数を呼び出してみよう
# 0 1 1 2 3 5 8 13 21 34 55 89 144 233 377 610 987 1597
fib(2000)
# <function fib at 0x0000026EA2BD5750>
print(fib)
f = fib
# 0 1 1 2 3 5 8 13 21 34 55 89
f(100)
#
fib(0)
# None
print(fib(0))
def fib2(n): # nまでのフィボナッチ級数を書き出す
"""nまでのフィボナッチ級数から成るリストを返す"""
result = []
a , b= 0, 1
while a < n:
result.append(a)
a, b = b, a+b
return result
f100 = fib2(100)
# [0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89]
print(f100)
4.7 さらに関数定義について
4.7.1 引数のデフォルト値
def ask_ok(prompt, retries=4, reminder='Please try again!'):
while True:
ok = input(prompt)
if ok in ('y', 'ye', 'yes'):
return True
if ok in ('n', 'no', 'nop', 'nope'):
return False
retries = retries - 1
if retries < 0:
raise ValueError('invalid user response')
print(reminder)
ask_ok('Do you really want to quit?')
ask_ok('OK to overwrite the file?', 2)
ask_ok('OK to overwrite the file?', 2, 'Come on, only yes or no')
i = 5
def f(arg=i):
print(arg)
i = 6
# 5
f()
def f(a, L=[]):
L.append(a)
return L
# [1]
# [1, 2]
# [1, 2, 3]
print(f(1))
print(f(2))
print(f(3))
def f(a, L=None):
if L is None:
L = []
L.append(a)
return L
# [1]
# [2]
# [3]
print(f(1))
print(f(2))
print(f(3))
4.7.2 キーワード引数
def parrot(voltage, state='a stiff', action='voom',
type='Norwegian Blue'):
print("-- This parrot wouldn't", action, end=' ')
print("if you put", voltage, "voltes through it.")
print("-- Lovely plumage, the", type)
print("-- It's", state, "!")
# -- This parrot wouldn't voom if you put 1000 voltes through it.
# -- Lovely plumage, the Norwegian Blue
# -- It's a stiff !
parrot(1000)
# -- This parrot wouldn't voom if you put 1000 voltes through it.
# -- Lovely plumage, the Norwegian Blue
# -- It's a stiff !
parrot(voltage=1000)
# -- This parrot wouldn't V00000M if you put 1000000 voltes through it.
# -- Lovely plumage, the Norwegian Blue
# -- It's a stiff !
parrot(voltage=1000000, action='V00000M')
# -- This parrot wouldn't V00000M if you put 1000000 voltes through it.
# -- Lovely plumage, the Norwegian Blue
# -- It's a stiff !
parrot(action='V00000M', voltage=1000000)
# -- This parrot wouldn't jump if you put a million voltes through it.
# -- Lovely plumage, the Norwegian Blue
# -- It's bereft of life !
parrot('a million', 'bereft of life', 'jump')
# -- This parrot wouldn't voom if you put a thousand voltes through it.
# -- Lovely plumage, the Norwegian Blue
# -- It's pushing up the daisies !
parrot('a thousand', state='pushing up the daisies')
# しかし次のようなコールは無効である：
# parrot() #必要な引数がない
# parrot(voltage=5.0, 'dead') # キーワード引数の後に非キーワード引数
# parrot(110, voltage=220) # 同じ引数に値を2度与えた
# parrot(actor='John Cleese') # 未知のキーワード引数
def function(a):
pass
# エラー
# function(0, a=0)
def cheeseshop(kind, *arguments, **keywords):
print("-- Do you have any", kind, "?")
print("-- I'm sorry, we'", kind, "?")
for arg in arguments:
print(arg)
print("-" * 40)
for kw in keywords:
print(kw, ":", keywords[kw])
# It's very runny, sir.
# It's really very, VERY runny, sir.
# ----------------------------------------
# shopkeeper : Michael Palin
# client : John Cleese
# sketch : Cheese Shop Sketch
cheeseshop("Limburger", "It's very runny, sir.",
"It's really very, VERY runny, sir.",
shopkeeper="Michael Palin",
client="John Cleese",
sketch="Cheese Shop Sketch")
4.7.3 特殊引数
def f (pos1, pos2, / , pos_or_kwd, * , kwd1, kwd2):
pass
def standard_arg(arg):
print(arg)
def pos_only_arg(arg, /):
print(arg)
def kwd_only_arg(*, arg):
print(arg)
def combined_example(pos_only, / , standard, *, kwd_only):
print(pos_only, standard, kwd_only)
# 2
standard_arg(2)
# 2
standard_arg(arg=2)
# 1
pos_only_arg(1)
# エラー
# pos_only_arg(arg=1)
# エラー
# kwd_only_arg(3)
# 3
kwd_only_arg(arg=3)
# エラー
# combined_example(1, 2, 3)
# 1 2 3
combined_example(1, 2, kwd_only=3)
# 1 2 3
combined_example(1, standard=2, kwd_only=3)
# エラー
# combined_example(pos_only=1, standard=2, kwd_only=3)
def foo(name, **kwds):
return 'name' in kwds
# エラー
# foo(1,**{'name': 2})
def foo(name, /, **kwds):
return 'name' in kwds
f = foo(1,**{'name': 2})
# True
print(f)
4.7.4 任意引数のリスト
def write_multiple_items(file, separator, *args):
file.write(separator.join(args))
def concat(*args, sep="/"):
return sep.join(args)
a = concat("earth", "mars", "venus")
# earth/mars/venus
print(a)
b = concat("earth", "mars", "venus", sep=".")
# earth.mars.venus
print(b)
4.7.5 引数リストのアンパック
a = list(range(3,6)) # 個別の引数を使った普通のコール
# [3, 4, 5]
print(a)
args = [3, 6]
b = list(range(*args)) # リストからアンパックした引数でコール
# [3, 6]
print(b)
def parrot(voltage, state='a stiff', action='voom'):
print("-- This parrot would't", action, end=' ')
print("If you put", voltage, "volts through it.", end= ' ')
print("E's", state, "!")
d = {"voltage": "four million", "state": "bleedin' demised", "action": "VOOM"}
# -- This parrot would't VOOM If you put four million volts through it. E's bleedin' demised !
parrot(**d)
4.7.6 lambda（ラムダ）式
def make_incrementor(n):
return lambda x: x + n
f = make_incrementor(42)
a = f(0)
# 42
print(a)
b = f(1)
# 43
print(b)
c = f(2)
# 44
print(c)
#こういう使い方もできるはず
# 32
print(make_incrementor(20)(12))
pairs = [(1, 'one'), (2, 'two'), (3, 'three'), (4, 'four')]
pairs.sort(key=lambda pair: pair[1])
# [(4, 'four'), (1, 'one'), (3, 'three'), (2, 'two')]
print(pairs)
4.7.7 ドキュメンテーション文字列(docstring)
def my_function():
"""Do nothing, but document it.
No, really, it doesn't do anything.
"""
pass
# Do nothing, but document it.
#
# No, really, it doesn't do anything.
print(my_function.__doc__)
4.7.8 関数注釈（関数アノテーション）
def f(ham: str, eggs: str = 'eggs') -> str:
print("Annotations:", f.__annotations__)
print("Arguments:", ham, eggs)
return ham + ' and ' + eggs
# Annotations: {'ham': <class 'str'>, 'eggs': <class 'str'>, 'return': <class 'str'>}
# Arguments: spam eggs
a = f('spam')
# spam and eggs
print(a)