Qiita Teams that are logged in
You are not logged in to any team

Community
Service
Qiita JobsQiita ZineQiita Blog
5
Help us understand the problem. What are the problem?

More than 3 years have passed since last update.

@ishigero

# 【備忘】Effective Python 1章（スライス、リスト内包表記、lambda）

Pythonicな箇所をピックアップして残そうと思います。
これからPythonを勉強しようと思っている方にも役立つかもしれないです。

# シーケンスのスライス

``````nums = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

print('first four:', nums[:4])      # first four: [0, 1, 2, 3]
print('last four:', nums[-4:])      # last four: [7, 8, 9, 10]
print('middle two:', nums[3:-3])    # middle two: [3, 4, 5, 6, 7]

print(nums[:])        # [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
print(nums[:5])       # [0, 1, 2, 3, 4]
print(nums[:-1])      # [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
print(nums[4:])       # [4, 5, 6, 7, 8, 9, 10]
print(nums[-3:])      # [8, 9, 10]
print(nums[2:5])      # [2, 3, 4]
print(nums[2:-1])     # [2, 3, 4, 5, 6, 7, 8, 9]
print(nums[-3:-1])    # [8, 9]
``````

スッキリ書ける。

# リスト内包表記とlambda

``````nums = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
``````

リスト内包表記

``````[x**2 for x in nums]
# [1, 4, 9, 16, 25, 36, 49, 64, 81, 100]
``````

lambda

``````list(map(lambda x: x**2, nums))
# [1, 4, 9, 16, 25, 36, 49, 64, 81, 100]
``````

``````[x**2 for x in nums if x % 2 == 0]
# [4, 16, 36, 64, 100]
``````

filterを使いlambdaでも表現できる

``````list(map(lambda x: x**2, filter(lambda x: x % 2 == 0, nums)))
# [4, 16, 36, 64, 100]
``````

``````chile_ranks = {'ghost': 1, 'habanero': 2, 'cayenne': 3}
{rank: name for name, rank in chile_ranks.items()}
# {1: 'ghost', 2: 'habanero', 3: 'cayenne'}

{len(name) for name in rank_dict.values()}
# {8, 5, 7}
``````

lambdaは少し可読性が下がる。

・appendメソッドの呼び出し部分のオーバーヘッド
・for文はループする度にリストオブジェクトのappendを参照する
・for文はappendをpythonの関数として実行する

Why not register and get more from Qiita?
1. We will deliver articles that match you
By following users and tags, you can catch up information on technical fields that you are interested in as a whole
2. you can read useful information later efficiently
By "stocking" the articles you like, you can search right away
5
Help us understand the problem. What are the problem?