当我减去两个词典时，继续收到错误：TypeError：不支持的操作数类型 - ：'dict'和'float'

Question

def duration_in_mins(datum, city):
    """
    Takes as input a dictionary containing info about a single trip (datum) and
    its origin city (city) and returns the trip duration in units of minutes.

    Remember that Washington is in terms of milliseconds while Chicago and NYC
    are in terms of seconds. 

    HINT: The csv module reads in all of the data as strings, including numeric
    values. You will need a function to convert the strings into an appropriate
    numeric type when making your transformations.
    see https://docs.python.org/3/library/functions.html
    """
    datum_n = round(float(example_trips['NYC']['tripduration'])/60,4)
    print(datum_n)
    datum_c = round(float(example_trips['Chicago']['tripduration'])/60,4)
    print(datum_c)
    datum_w = round(float(example_trips['Washington']['Duration (ms)'])/60000,4)
    print(datum_w)

    duration={'NYC': datum_n,
              'Chicago': datum_c,
              'Washington': datum_w}

    print(duration)

    return duration

tests = {'NYC': 13.9833,
     'Chicago': 15.4333,
     'Washington': 7.1231}print(duration)

**for city in tests:
assert abs(duration_in_mins(example_trips[city], city) - tests[city]) < .001**

---

TypeError                                 Traceback (most recent call last)
<ipython-input-10-90486a3cfc17> in <module>()
     45 
     46 for city in tests:
---> 47     assert abs(duration_in_mins(example_trips[city], city) - tests[city]) < .001

TypeError: unsupported operand type(s) for -: 'dict' and 'float'

Answer 1

您正在比较dict和float。作为算术运算，不能将一个与另一个相反。

特别：

• duration_in_mins(example_trips[city], city)返回一个dict对象。
• tests[city]返回一个float对象。

我的猜测是你想要的：

duration_in_mins(example_trips[city], city)[city] - tests[city]