get() in get() method of Pyhon dict

Posted by Blog - uTIcARdI on January 9, 2019

Write down the tip for the practice: The Time in Words.

A dict was created for the time in number format to string format:

intToStrDict = {
        1: 'one',
        2: 'two',
        3: 'three',
        4: 'four',
        5: 'five',
        6: 'six',
        7: 'seven',
        8: 'eight',
        9: 'nine',
        10: 'ten',
        11: 'eleven',
        12: 'twelve',
        13: 'thirteen',
        14: 'fourteen',
        15: 'quarter',
        16: 'sixteen',
        17: 'seventeen',
        18: 'eighteen',
        19: 'nineteen',
        20: 'twenty',
        30: 'half',
        40: 'fourty',
        50: 'fifty'
    }

get() is a good way get the value of a key from the dict, so I tried following function to convert minute in number format to string format:

def minTowords(tempm):
    return intToStrDict.get(tempm, ' '.join([intToStrDict.get( tempm // 10 * 10), intToStrDict.get( tempm % 10 )])
    )

Unfortunately, it run into following error when the minute number is less than 10:

minTowords(3)

Traceback (most recent call last):
  File "/Users/kz/Documents/C/Pys/test.py", line 538, in <module>
    print(timeInWords(3, 1))
  File "/Users/kz/Documents/C/Pys/test.py", line 533, in timeInWords
    return "%s%s past %s" % (minTowords(m),'' if m in (15, 30) else ' minute' if m ==1 else ' minutes', intToStrDict[h])
  File "/Users/kz/Documents/C/Pys/test.py", line 522, in minTowords
    return intToStrDict.get(tempm, intToStrDict.get( tempm // 10 )+ ' '+intToStrDict.get( tempm % 10 ))
TypeError: unsupported operand type(s) for +: 'NoneType' and 'str'

It’s wired because 3 is defined in the dict already which means the default part : ’ ‘.join([intToStrDict.get( tempm // 10 * 10), intToStrDict.get( tempm % 10 )]) should not be executed.

For testing purpose, I modified the function to:

def minTowords(tempm):
    return intToStrDict.get(tempm, ' '.join([intToStrDict.get( tempm // 10 * 10), ''])
    )

with same error:

minTowords(3)

Traceback (most recent call last):
  File "/Users/kz/Documents/C/Pys/test.py", line 540, in <module>
    minTowords(3)
  File "/Users/kz/Documents/C/Pys/test.py", line 522, in minTowords
    return intToStrDict.get(tempm, ' '.join([intToStrDict.get( tempm // 10 * 10), ''])
TypeError: sequence item 0: expected str instance, NoneType found

To check if the list operation causes the issue, tried with

def minTowords(tempm):
    return intToStrDict.get(tempm, [intToStrDict.get( tempm // 10 * 10)])

it works. The root cause should be string operation: join()

Did another two testings for verification:

  • Join string with operator: ‘+’

    def minTowords(tempm):
        return intToStrDict.get(tempm, intToStrDict.get( tempm // 10 * 10) + ' ' + intToStrDict.get( tempm % 10 ))
    

    Doesn’t work

  • Remove Join operation

    def minTowords(tempm):
        return intToStrDict.get(tempm, [intToStrDict.get( tempm // 10 * 10), intToStrDict.get( tempm % 10 )])
    

    works

Finally, I made it by following code:

def minTowords(tempm):
    if tempm in intToStrDict:
        return intToStrDict[tempm]
    return ' '.join([intToStrDict.get( tempm // 10 * 10), intToStrDict.get( tempm % 10 )])

Summary:

Be careful when a function was taken as default parameter of the get() method.


get() in get() method of Pyhon dict


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