Creating a custom format specifier in format method in python

Question

I was implementing my own format specifiers by overriding the __format__() method in my class. Now the trouble that I am having is that I am getting the below error. Is it because I can not use %s for any other format specification other than str() or am I doing something wrong here.

Traceback (most recent call last): File "test.py", line 66, in print("Dealer has {0:%r of %s}".format(NumberCard(1, Club))) File "ch1.py", line 24, in format result = format_spec.replace("%r", self.rank).replace("%s", self.suit) TypeError: replace() argument 2 must be str, not int

class Card:

    insure = False

    def __init__(self, rank, suit):
        self.suit = suit
        self.rank = rank
        self.hard, self.soft = self._points()

    def __str__(self):
        return "{rank}{suit}".format(**self.__dict__)

    def __repr__(self):
        return "{__class__.__name__}(suit={suit!r}, rank={rank!r})".format(__class__=self.__class__, **self.__dict__)

    def __format__(self, format_spec):
        if format_spec == "":
            return str(self)
        else:
            result = format_spec.replace("%r", self.rank).replace("%s", self.suit)
            result = result.replace("%%", "%")
            return result

class NumberCard(Card):

    def _points(self):
        return int(self.rank), int(self.rank)


class Suit:

    def __init__(self, name, symbol):
        self.name = name
        self.symbol = symbol

I am passing my arguments as

print("Dealer has {0:%r of %s}".format(NumberCard(1, Suit('Club', '♣'))))

OneCricketeer · Accepted Answer · 2018-04-29 07:17:32Z

2

NumberCard(1, Suit('Club', '♣'))

So, the rank is an int

You're calling replace("%r", self.rank)

The error says replace() argument 2 must be str, not int

Use str(self.rank) in the replace instead

answered Apr 29, 2018 at 7:17

OneCricketeer

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Comments

Patrick Artner · Accepted Answer · 2018-04-29 07:15:20Z

1

Convert it?

def __format__(self, format_spec):
    if format_spec == "":
        return str(self)
    else:
        result = format_spec.replace("%r", str(self.rank)) # stringify your int
        result = result.replace("%s", str(self.suit.symbol)) # symbol instead class name
        result = result.replace("%%", "%")

Replace works on replace(str,str) - you can not replace a str with a int using it.

Doku: https://docs.python.org/3.6/library/stdtypes.html#str.replace

answered Apr 29, 2018 at 7:15

Patrick Artner

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