在Python 2.5中嵌套For Range循环传递参数

Question

我正在学习Python，想弄明白如何在'for range'循环中把一个参数传递给一个变量。在下面的代码中，我希望'months'变量能代表月份的名字（比如一月、二月等等）。然后我想让用户输入'sales'变量时提示'请输入一月的销售额'。接着在下一次循环时，提示变成'请输入二月的销售额'。

谢谢大家的建议。

def main():
    number_of_years = input('Enter the number of years for which you would like to compile data: ')
    total_sales = 0.0
    total_months = number_of_years * 12

    for years in range(number_of_years):
        for months in range(1, 13):
            sales = input('Enter sales: ')
            total_sales += sales

    print ' '        
    print 'The number of months of data is: ', total_months
    print ' '
    print 'The total amount of sales is: ', total_sales 
    print ' '
    average = total_sales / total_months    # variable to average results
    print 'The average monthly sales is: ', average

main()

Answer 1

你需要的是一种方法，可以把1到12的月份数字转换成月份的缩写名。虽然你可以用一个月份名称的列表来做到这一点，但要记得在使用之前总是要把月份数字减去1，因为列表的索引是从0开始的，而不是从1开始的。还有一种更简单的方法，就是使用Python的字典。

用字典的话，你的程序可能看起来像这样：

# construct dictionary
month_names = "Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec".split()
months = dict((i, month) for i, month in enumerate(month_names, 1))

def main():
    number_of_years = input('Enter the number of years for which '
                            'you would like to compile data: ')
    total_sales = 0.0
    total_months = number_of_years * 12

    for years in range(number_of_years):
        for month in range(1, 13):
            sales = input('Enter sales for %s: ' % months[month])
            total_sales += sales

    print
    print 'The number of months of data is: ', total_months
    print
    print 'The total amount of sales is: ', total_sales
    print
    average = total_sales / total_months    # variable to average results
    print 'The average monthly sales is: ', average

main()

除了添加months字典的构建，我还修改了你调用input()的部分，让用户提示显示月份的名称。

顺便说一下，你可能还想把打印平均值的语句改成：

    print 'The average monthly sales is: "%.2f"' % average

这样就只会显示小数点后两位数字（而不是更多）。

Answer 2

Python中的字典和列表这两个东西会让你走得很远。

>>> months = "Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec".split()
>>> sales = {}
>>> for num, name in enumerate(months, 1):
    print "Sales for", name
    sales[num] = 14.99 # get the sales here
    print "Num:", num

Sales for Jan
Num: 1
Sales for Feb
Num: 2
Sales for Mar
Num: 3
Sales for Apr
Num: 4
... etc.

>>> for month, price in sales.items():
    print month, "::", price

1 :: 14.99
2 :: 14.99
... etc.

>>> ave = sum(sales.values()) / float(len(sales)) # average sales