Python自定义格式化程序

我正在写一个程序来处理不同月份到期的合同

例如，2016年12月到期的玉米期货合同将被称为：

CZ2016

其中C表示“玉米”，Z表示十二月（这是习俗）

在内部，我将所有内容表示为

（年、月）

每种合同类型都有不同的格式，理想情况下，我需要能够双向执行

目前，我已经编写了一些详细的字符串处理来实现这一点，但这是一个混乱

做这件事最具蟒蛇风格的方式是什么？

这里有一些快速的方法：

这里有一些快速的信息：

---

就我个人而言，我会写一个

\uuuuuuuuuuuuuuuuuuuuuuuuu

神奇的方法（假设每个契约都由一个自定义类的实例表示。这样，您就可以简单地使用print来输出write格式。创建一个带有接受字符串的c'tor的类，以及一个

\uuuuuuuuuuuuuuuuuuu>方法来返回类似字符串？我个人会编写一个
\uuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuu格式
魔术方法（假设每个契约都由一个自定义类的实例表示。这样，您就可以简单地使用print输出写入格式。创建一个带有接受字符串的c'tor的类，并使用
\u str\u
方法返回类似的字符串？哦，天哪，这太神奇了！谢谢！告诉我您编写这个不是为了这个问题吗？：）哦，天哪，这太棒了！谢谢！告诉我你写这篇文章不是为了这个问题吗？：）
#!python3
import collections
import time

class FuturesContract:
    Commodity = collections.namedtuple('Commodity',
            'symbol future exchange delivery_months')

    Commodities = [
        # Source: http://www.mrci.com/web/online-explanation-pages/symbols-a-codes.html
        # !IMPORTANT! Sorted by length of symbol!!!
        Commodity('ITCO', 'Brent Crude', 'ICE', 'F,G,H,J,K,M,N,Q,U,V,X,Z'),
        Commodity('AD', 'Australian Dollar', 'CME', 'H,M,U,Z'),
        Commodity('BP', 'British Pound', 'CME', 'H,M,U,Z'),
        Commodity('CD', 'Canadian Dollar', 'CME', 'H,M,U,Z'),
        Commodity('DX', 'US Dollar Index', 'ICE', 'H,M,U,Z'),
        Commodity('EU', 'EuroFx', 'CME', 'H,M,U,Z'),
        Commodity('JY', 'Japanese Yen', 'CME', 'H,M,U,Z'),
        Commodity('SF', 'Swiss Franc', 'CME', 'H,M,U,Z'),
        Commodity('CL', 'Crude Oil', 'NYM', 'F,G,H,J,K,M,N,Q,U,V,X,Z'),
        Commodity('HO', 'NY Harbor ULSD/Heating Oil', 'NYM', 'F,G,H,J,K,M,N,Q,U,V,X,Z'),
        Commodity('HU', 'Unleaded Gas', 'NYM', 'F,G,H,J,K,M,N,Q,U,V,X,Z'),
        Commodity('NG', 'Natural Gas', 'NYM', 'F,G,H,J,K,M,N,Q,U,V,X,Z'),
        Commodity('RB', 'RBOB Gasoline', 'NYM', 'F,G,H,J,K,M,N,Q,U,V,X,Z'),
        Commodity('BO', 'Soybean Oil', 'CBOT', 'F,H,K,N,Q,U,V,Z'),
        Commodity('KW', 'Kansas City Wheat', 'KCBT', 'H,K,N,U,Z'),
        Commodity('MW', 'Minneapolis Wheat', 'MGE', 'H,K,N,U,Z'),
        Commodity('SM', 'Soybean Meal', 'CBOT', 'F,H,K,N,Q,U,V,Z'),
        Commodity('DJ', 'Dow Jones Industrials', 'CBOT', 'H,M,U,Z'),
        Commodity('KV', 'Value Line (Discontinued)', 'KCBT', 'H,M,U,Z'),
        Commodity('MV', 'Value Line (Mini)', 'KCBT', 'H,M,U,Z'),
        Commodity('ND', 'Nasdaq-100', 'CME', 'H,M,U,Z'),
        Commodity('RL', 'Russell 2000 (Discontinued)', 'CME', 'H,M,U,Z'),
        Commodity('SP', 'S & P 500', 'CME', 'H,M,U,Z'),
        Commodity('YU', 'NYSE Composite (Discontinued)', 'NYFE', 'H,M,U,Z'),
        Commodity('ED', 'Eurodollars', 'CME', 'H,M,U,Z'),
        Commodity('FV', '5-Yr T-Notes', 'CBOT', 'H,M,U,Z'),
        Commodity('MB', 'Municipal Bonds', 'CBOT', 'H,M,U,Z'),
        Commodity('TU', '2-Yr T-Notes', 'CBOT', 'H,M,U,Z'),
        Commodity('TY', '10-Yr T-Notes', 'CBOT', 'H,M,U,Z'),
        Commodity('US', '30-Yr T-Bonds', 'CBOT', 'H,M,U,Z'),
        Commodity('FC', 'Feeder Cattle', 'CME', 'F,H,J,K,Q,U,V,X'),
        Commodity('LC', 'Live Cattle', 'CME', 'G,J,M,Q,V,Z'),
        Commodity('LH', 'Lean Hogs', 'CME', 'G,J,K,M,N,Q,V,Z'),
        Commodity('LE', 'Lean Hogs', 'CME', 'G,J,K,M,N,Q,V,Z'),
        Commodity('PB', 'Pork Bellies', 'CME', 'G,H,K,N,Q'),
        Commodity('DA', 'Milk Class III', 'CME', 'F,G,H,J,K,M,N,Q,U,V,X,Z'),
        Commodity('GC', 'Gold', 'CMX', 'G,J,M,Q,V,Z'),
        Commodity('HG', 'Copper', 'CMX', 'H,K,N,U,Z'),
        Commodity('PL', 'Platinum', 'NYM', 'F,J,N,V'),
        Commodity('SI', 'Silver', 'CMX', 'H,K,N,U,Z'),
        Commodity('RR', 'Rice', 'CBOT', 'F,H,K,N,U,X'),
        Commodity('CC', 'Cocoa', 'ICE', 'H,K,N,U,Z'),
        Commodity('CT', 'Cotton', 'ICE', 'H,K,N,V,Z'),
        Commodity('KC', 'Coffee', 'ICE', 'H,K,N,U,Z'),
        Commodity('LB', 'Lumber', 'CME', 'F,H,K,N,U,X'),
        Commodity('JO', 'Orange Juice', 'ICE', 'F,H,K,N,U,X'),
        Commodity('SB', 'Sugar #11', 'ICE', 'H,K,N,V'),
        Commodity('C', 'Corn', 'CBOT', 'F,H,K,N,U,X,Z'),
        Commodity('O', 'Oats', 'CBOT', 'H,K,N,U,Z'),
        Commodity('S', 'Soybeans', 'CBOT', 'F,H,K,N,Q,U,X'),
        Commodity('W', 'Wheat', 'CBOT', 'H,K,N,U,Z'),
    ]

    Months = {
        1: 'January',
        2: 'February',
        3: 'March',
        4: 'April',
        5: 'May',
        6: 'June',
        7: 'July',
        8: 'August',
        9: 'September',
        10: 'October',
        11: 'November',
        12: 'December',
        'F': 'January',
        'G': 'February',
        'H': 'March',
        'J': 'April',
        'K': 'May',
        'M': 'June',
        'N': 'July',
        'Q': 'August',
        'U': 'September',
        'V': 'October',
        'X': 'November',
        'Z': 'December',
    }

    MonthCodes = {
        'January': 'F',
        'February': 'G',
        'March': 'H',
        'April': 'J',
        'May': 'K',
        'June': 'M',
        'July': 'N',
        'August': 'Q',
        'September': 'U',
        'October': 'V',
        'November': 'X',
        'December': 'Z',
    }

    def __init__(self, details=None):
        if details is None:
            now = time.localtime()
            month = now.tm_mon
            year = now.tm_year
            self.commodity = None
        else:
            for c in self.Commodities:
                if details.startswith(c.symbol):
                    self.commodity = c
                    symlen = len(c.symbol)
                    month = details[symlen:symlen+1]
                    year = details[symlen+1:]
                    if len(year) == 2:
                        year = '20'+year
                    year = int(year)
                    break
            else:
                raise ValueError("Unparseable details given: "+details)

        month = self.Months[month]
        if self.commodity is not None:
            month_code = self.MonthCodes[month]
            if month_code not in self.commodity.delivery_months:
                raise ValueError('Invalid delivery month for commodity: '+month)

        self.month = month
        self.year = year

    def __str__(self):
        c = self.commodity
        return 'Unspecified' if c is None else c.symbol + self.MonthCodes[self.month] + str(self.year)


    def explain(self):
        c = self.commodity
        return [ 'A FuturesContract for:',
                '\t{}: {} (on the {} exchange)'.format(c.symbol, c.future, c.exchange),
                '\tDated: {} ({}), {}'.format(self.month, self.MonthCodes[self.month], self.year),
                ]

cz2016 = FuturesContract('CZ2016')

print('\n'.join(cz2016.explain()))
print('\n')
print('Commodity:', cz2016.commodity)
print('Month:', cz2016.month)
print('Year:', cz2016.year)

print("\nHas __str__:", cz2016)

print("\n\n")
print("Future LBQ2014: (should be invalid, because Q):")
fc = FuturesContract('LBQ2014')