背景

CodeWar上的一道原题，通过格式划字符串精简了代码结构，省去了很多条件判断语句。

题目描述

Your task in order to complete this Kata is to write a function which formats a duration, given as a number of seconds, in a human-friendly way.

The function must accept a non-negative integer. If it is zero, it just returns “now”. Otherwise, the duration is expressed as a combination of years, days, hours, minutes and seconds.

It is much easier to understand with an example:

format_duration(62) # returns “1 minute and 2 seconds”
format_duration(3662) # returns “1 hour, 1 minute and 2 seconds”

Note that spaces are important.

Detailed rules

The resulting expression is made of components like 4 seconds, 1 year, etc. In general, a positive integer and one of the valid units of time, separated by a space. The unit of time is used in plural if the integer is greater than 1.

The components are separated by a comma and a space (“, “). Except the last component, which is separated by ” and “, just like it would be written in English.

A more significant units of time will occur before than a least significant one. Therefore, 1 second and 1 year is not correct, but 1 year and 1 second is.

Different components have different unit of times. So there is not repeated units like in 5 seconds and 1 second.

A component will not appear at all if its value happens to be zero. Hence, 1 minute and 0 seconds is not valid, but it should be just 1 minute.

A unit of time must be used “as much as possible”. It means that the function should not return 61 seconds, but 1 minute and 1 second instead. Formally, the duration specified by of a component must not be greater than any valid more significant unit of time.

For the purpose of this Kata, a year is 365 days and a day is 24 hours.

解题思路

题目是很简单的，关键是如何优雅地完成是否在当前时间单位后添加’s’和’,’或者’and’，我的代码里运用了很多

true_value if condition else false_value

语句。

代码

def format_duration(seconds):
    if seconds == 0: return "now"
    origin = seconds
    dic = {
        'year': 60 * 60 * 24 * 365,
        'day': 60 * 60 * 24,
        'hour': 60 * 60,
        'minute': 60,
        'second': 1
    }
    spent = {}
    ans = ""
    for x in ['year','day','hour','minute','second']:
        spent[x] = seconds // dic[x]
        ans += "{}{} {}{}".format('' if seconds == origin else ' and ' if seconds % dic[x] == 0 else ', ',spent[x],x,'s' if spent[x] > 1 else '') if spent[x] > 0 else ''
        seconds %= dic[x]
    return  ans

感想

if else 表达式真是一个神器。