添加日期，检查是否过期

Question

我程序的一个部分需要用户输入一个日期，然后这个日期会和字典里每个产品的到货日期进行比较，看看这个产品的保质期加上到货日期，是在用户输入的日期之前过期，还是之后过期。

import sys
from string import *
import pickle
import datetime

cheeseDictionary = {}
userInput = ""

def loadProduct(fileName):
    global cheeseDictionary
    f = open(fileName,"r")
    line = f.readline()         # Reads line from file
    while line:
        line = line[:-1]
        data = split(line,":")  # Splits line when there is a colon
        cheeseDictionary[data[0]] = {"date":data[1], "life":data[2], "name":data[3]} # Stores each split item
        line = f.readline()     # Next line
    f.close()

def saveProduct(fileName,cheeseDictionary): 
    f = open(fileName, "w")
    for i in sorted(cheeseDictionary.keys()):
        v = cheeseDictionary[i]
        f.write("%s:%s:%s:%s\n" % (i, v["date"], v["life"], v["name"]))
    f.close()

def printProduct(cheeseDictionary):
    print "ID"," ","Date"," ","Life(days)"," ","Name"
    for cheese in cheeseDictionary:
        print cheese," ",cheeseDictionary[cheese]["date"]," ",cheeseDictionary[cheese]["life"],"    ",cheeseDictionary[cheese]["name"]

def addProduct():
    global cheeseDicitonary
    correct = 0
    idInput = ""
    dateInput = ""
    lifeInput = ""
    nameinput = ""

    while correct != 1:
        idInput = raw_input("Please enter the ID of the cheese to be added. ")
        if cheeseDictionary.has_key(idInput):
            print ("This ID already exists. Please try again.")
            correct = 0
        else:
            newID = idInput
            correct = 1
    dateInput = raw_input("Please enter the date of the cheese to be added in the format dd/mm/yyyy. ")
    lifeInput = raw_input("Please enter the life of the cheese to be added in days. ")
    nameInput = raw_input("Please enter the name of the cheese to be added. ")
    cheeseDictionary[idInput] = {"date":dateInput, "life":lifeInput, "name":nameInput}

def checkProduct(cheeseDictionary):
    dateCheck = raw_input("Please enter the date in the format dd/mm/yyyy: ")
    for cheese in cheeseDictionary:

我知道我需要把字典里存储的日期转换成日期时间格式，但我不太确定该怎么做。谢谢大家的建议。:)

Answer 1

为了好玩，我做了一个相当全面的面向对象的重写：

import datetime

class Date(object):
    def __init__(self, s):
        if isinstance(s, Date):
            self.date = s.date
        elif isinstance(s, datetime.date):
            self.date = s
        else:
            self.date = datetime.datetime.strptime(s, "%d/%m/%Y")

    def __add__(self, val):
        if isinstance(val, Life):
            val = val.life
        elif not isinstance(val, datetime.timedelta):
            val = datetime.timedelta(val)
        return self.__class__(self.date + val)

    def __cmp__(self, val):
        return (self.date - val.date).days

    def __str__(self):
        return self.date.strftime("%d/%m/%Y")

class Life(object): 
    def __init__(self, s):
        if isinstance(s, Life):
            self.life = s.life
        elif isinstance(s, datetime.timedelta):
            self.life = s
        else:
            self.life = datetime.timedelta(days=int(s))

    def __str__(self):
        return str(self.life.days)

class Product(object):
    FMT = "{0:10} {1:10} {2:24}".format

    def __init__(self, date, life, name):
        super(Product,self).__init__()
        self.date = Date(date)
        self.life = Life(life)
        self.name = str(name).strip()

    def __str__(self):
        return Product.FMT(self.date, self.life, self.name)

    def expires(self):
        return Date(self.date + self.life)

    @classmethod
    def get(cls):
        date = getClass(Date, "Please enter the date (DD/MM/YYYY): ")
        life = getClass(Life, "Please enter the life (in days): ")
        name = raw_input("Please enter the name of the cheese: ")
        return cls(date, life, name)

    def vals(self):
        return self.date, self.life, self.name

class FileOf(object):
    def __init__(self, cls):
        self.data = {}
        self.cls  = cls

    def loadFile(self, fname, mode='r', sep=':'):
        _data = self.data
        _cls  = self.cls
        with open(fname, mode) as inf:
            for line in inf:
                try:
                    items = line.strip().split(sep)
                    id = items.pop(0)
                    _data[id] = _cls(*items)
                except ValueError, e:
                    print(e)
        return self

    def saveFile(self, fname, mode='w', sep=':', eol='\n', key=None):
        _data = self.data
        keys = _data.keys()
        keys.sort(key=key)
        with open(fname, mode) as outf:
            for id in keys:
                outf.write(str(id)+sep)
                outf.write(sep.join(str(v) for v in _data[id].vals()))
                outf.write(eol)
        return self

    def addNew(self):
        id  = getNewKey(self.data, "Please enter the new ID: ")
        obj = getClass(self.cls)
        self.data[id] = obj
        return self

    def printAll(self, key=None):
        _data = self.data
        _cls  = self.cls
        ID = "{0:4} ".format
        print ID("id") + _cls.FMT("Date", "Life", "Name")
        keys = _data.keys()
        keys.sort(key=key)
        for id in keys:
            print ID(id) + _cls.FMT(*(_data[id].vals()))
        return self

    def filter(self, filterFn):
        newFile = FileOf(self.cls)
        newFile.data = {id:item for id,item in self.data.iteritems() if filterFn(id, item)}
        return newFile

def getNewKey(keys, msg='', keytype=str):
    "Prompt for a key not already in keys"
    while True:
        key = keytype(raw_input(msg))
        if key in keys:
            print("This key already exists. Please try again.")
        else:
            return key

def getClass(cls, *args, **kwargs):
    "Return a new instance of given class; prompt for required values"
    if hasattr(cls, 'get'):
        # if the class knows how to 'get' itself, let it
        return cls.get(*args, **kwargs)
    else:
        # otherwise we assume the class knows how to init itself from a string
        while True:
            s = raw_input(*args)
            try:
                return cls(s, **kwargs)
            except ValueError, e:
                print(e)

def getExpired(cheeses, asOf=None):    
    asOf = Date(asOf) if asOf else getClass(Date, "Please enter expiration test date (DD/MM/YYYY): ")
    return cheeses.filter(lambda id,obj: obj.expires() <= asOf)

def main():
    cheeses = FileOf(Product).loadFile('cheesefile.txt')
    cheeses.printAll()

    cheeses.addNew()

    expiredA = getExpired(cheeses)                 # prompt for expiration date
    expiredB = getExpired(cheeses, "12/3/2011")    # use given date

    print("The expired items are:")
    expiredB.printAll()

    cheeses.saveFile('cheesefile.txt')

if __name__=="__main__":
    main()

还有一个示例 cheesefile.txt 文件：

ab:03/01/2011:10:brie
ac:03/01/2001:20:camembert
de:01/03/2011:30:brie
fg:01/03/2011:1:blink and it's gone
hi:01/05/2011:200:hard white cheddar
jkl:01/04/2011:60:jarlsberg

Answer 2

为了把一个日期字符串转换成一个 datetime 对象，你可以使用 strptime 方法：

http://www.tutorialspoint.com/python/time_strptime.htm

几乎你需要知道的关于Python的所有信息都可以在文档中找到。这是 datetime 的文档：

http://docs.python.org/library/datetime.html

至于日期的数学运算（加法和减法），你可以通过给 datetime 对象加上或减去一个 timedelta 对象来实现。这里是允许的操作：

datetime2 = datetime1 + timedelta
datetime2 = datetime1 - timedelta
timedelta = datetime1 - datetime2
datetime1 < datetime2

所有的细节可以在上面链接的文档页面找到。

还有一个关于日期数学运算的小教程：

http://phr0stbyte.blogspot.com/2008/08/python-datetime-math.html

Answer 3

如果我理解得没错的话，你是想把表示日期的字符串，比如“dd/mm/yyyy”这种格式，转换成日期时间对象，对吧？

如果是这样的话，你可以使用 datetime.strptime 这个方法。举个例子：

from datetime import datetime
d = datetime.strptime("28/03/2011", "%d/%m/%Y")
print repr(d)

这样会输出：

datetime.datetime(2011, 3, 28, 0, 0)