Python自定义格式化程序

Question

我正在写一个程序来处理不同月份到期的合同。你知道吗

例如，2016年12月到期的玉米期货合约将被称为：

CZ2016

其中C表示“玉米”，Z表示十二月（这是习俗）。你知道吗

在内部，我将一切表示为(year, month)。你知道吗

每种合同类型都有不同的格式，理想情况下，我需要能够向两个方向发展。你知道吗

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。你知道吗

做这件事最像Python的方法是什么？你知道吗

Answer 1

有件事很快就发生了：

#!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')