のりよし関数
[のりよし Advent Calendar 2017](https://adventar.org/calendars/2192)の2日目の記事です。

```python
WEEKS_PER_YEAR = 52

# のりよしがこれまでにGBに使った金額(円)を計算する
def noriyoshi(
        # 平均支払い金額(円)
        payment,

        # 一週間あたりの平均GB回数
        gbs_per_week,

        # GBに行きはじめてからの年数
        years):
    """Return total payment of GB

    >>> noriyoshi(payment=1000, gbs_per_week=2, years=3)
    312000
    >>> noriyoshi(payment=500, gbs_per_week=2, years=3)
    Traceback (most recent call last):
     ...
    ValueError: noriyoshi must pay more than 1000 yen for GB
    >>> noriyoshi(payment=1000, gbs_per_week=0, years=3)
    Traceback (most recent call last):
     ...
    ValueError: noriyoshi must go to 1 GB per week
    >>> noriyoshi(payment=1000, gbs_per_week=2, years=1)
    Traceback (most recent call last):
     ...
    ValueError: niriyoshi must have GB experience over 3 years
    """
    if payment < 1000:
        raise ValueError("noriyoshi must pay more than 1000 yen for GB")
    if gbs_per_week < 1:
        raise ValueError("noriyoshi must go to 1 GB per week")
    if years < 3:
        raise ValueError("niriyoshi must have GB experience over 3 years")
    return payment * gbs_per_week * years * WEEKS_PER_YEAR

if __name__ == '__main__':
    import doctest
    doctest.testmod()
```

```bash
$ python3
Python 3.6.0 (default, Feb 16 2017, 02:21:07)
[GCC 4.2.1 Compatible Apple LLVM 8.0.0 (clang-800.0.38)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import noriyoshi
>>> noriyoshi.noriyoshi(payment=3000, gbs_per_week=2, years=5)
1560000
>>>
```
<span style="font-size: 200%;">
<span style="color: #ef0606">のりよしがこれまでにGBに使った金額は、推定_156万円_です</span></span>

明日は[やすさん](https://twitter.com/yatmsu)の、のりよしです。