Python 集合知プログラミング 写経(reloadについて)

* [O'Reilly 集合知プログラミング](https://www.oreilly.co.jp/books/9784873113647/) を写経しようと思ったがいきなりハマったのでメモ
  * 2-2 ～ 2-3-1 辺り  

# 書籍の通りに実行 ⇒ 失敗

* 以下のファイルを作る

```recommendations.py
critics={'Lisa Rose': {'Lady in the Water': 2.5, 'Snakes on a Plane': 3.5,
 'Just My Luck': 3.0, 'Superman Returns': 3.5, 'You, Me and Dupree': 2.5, 
 'The Night Listener': 3.0},
'Gene Seymour': {'Lady in the Water': 3.0, 'Snakes on a Plane': 3.5, 
 'Just My Luck': 1.5, 'Superman Returns': 5.0, 'The Night Listener': 3.0, 
 'You, Me and Dupree': 3.5}, 
'Michael Phillips': {'Lady in the Water': 2.5, 'Snakes on a Plane': 3.0,
 'Superman Returns': 3.5, 'The Night Listener': 4.0},
'Claudia Puig': {'Snakes on a Plane': 3.5, 'Just My Luck': 3.0,
 'The Night Listener': 4.5, 'Superman Returns': 4.0, 
 'You, Me and Dupree': 2.5},
'Mick LaSalle': {'Lady in the Water': 3.0, 'Snakes on a Plane': 4.0, 
 'Just My Luck': 2.0, 'Superman Returns': 3.0, 'The Night Listener': 3.0,
 'You, Me and Dupree': 2.0}, 
'Jack Matthews': {'Lady in the Water': 3.0, 'Snakes on a Plane': 4.0,
 'The Night Listener': 3.0, 'Superman Returns': 5.0, 'You, Me and Dupree': 3.5},
'Toby': {'Snakes on a Plane':4.5,'You, Me and Dupree':1.0,'Superman Returns':4.0}}
```

* 実行

```bash
$ python
>>> from recommendations import critics
>>> critics['Lisa Rose']['Lady in the Water']
2.5
```

* インタプリタは実行中のまま、ファイルに追記する
  * 下記のコードはサンプルのまま

```recommendations.py
from math import sqrt

# Returns a distance-based similarity score for person1 and person2
def sim_distance(prefs,person1,person2):
  # Get the list of shared_items
  si={}
  for item in prefs[person1]: 
    if item in prefs[person2]: si[item]=1

  # if they have no ratings in common, return 0
  if len(si)==0: return 0

  # Add up the squares of all the differences
  sum_of_squares=sum([pow(prefs[person1][item]-prefs[person2][item],2) 
                      for item in prefs[person1] if item in prefs[person2]])

  return 1/(1+sum_of_squares)
```

* 実行(続き)

```bash
>>> reload(recommendations)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'reload' is not defined
```

* できない！！ :sob: 

# 解決

## 解決までの流れ

* 誤記が多いらしい → [正誤表](https://sites.google.com/site/prgclctintelligence/errata) より `import recommendations`してみる

```bash
>>> import recommendations
>>> reload(recommendations)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'reload' is not defined
```

* 書籍はpython `2.4.1` → 実行環境は`3.6.5`
  * [#importlib.reload](https://docs.python.jp/3/library/importlib.html#importlib.reload)
  * [モジュールのリロード](https://qiita.com/tag1216/items/486ff0737fcb8cd0b7ac#%E3%83%A2%E3%82%B8%E3%83%A5%E3%83%BC%E3%83%AB%E3%81%AE%E3%83%AA%E3%83%AD%E3%83%BC%E3%83%89)

```bash
>>> import importlib
>>> importlib.reload(recommendations)
<module 'recommendations' from '/hoge/recommendations.py'>
>>> recommendations.sim_distance(recommendations.critics,'Lisa Rose','Gene Seymour')
0.14814814814814814
```

* できた！ :smile: 

## 結局どうすれば良かったか

```bash
>>> import recommendations
>>> import importlib
>>> importlib.reload(recommendations)
<module 'recommendations' from '/hoge/recommendations.py'>
>>> recommendations.sim_distance(recommendations.critics,'Lisa Rose','Gene Seymour')
0.14814814814814814
```



# 参考

* [O'Reilly 集合知プログラミング](https://www.oreilly.co.jp/books/9784873113647/)
  * [正誤表](https://sites.google.com/site/prgclctintelligence/errata)
  * [サンプルプログラム](https://resources.oreilly.com/examples/9780596529321)