string formatting with modulus/percent sign

Question

Is there something happening when string formatting that uses the modulus function while calling either

StringOperand % TupleOperand or

StringOperand % DictionaryOperand

Or is it just an arbitrary use of % for the string formatting function?

I'm guessing that the string formatting operator is not a call to modular arithmetic as the following:

tuple = (1,2,3)
print '%d %d %d'%tuple

prints: 1 2 3, but

print '%d %d %d %d'%tuple

returns TypeError: not enough args for format str

This is called *operator overloading* and is common in python. A class can implement an operator to mean anything it likes by implementing a special method, in this case `__mod__()`. For example, try `print "hello" * 3`. See also https://docs.python.org/2/library/operator.html — cdarke, Apr 06 '16 at 07:50

Rudziankoŭ · Accepted Answer · 2016-04-06T08:23:28.087

3

This is operator overloading. What you are talking about is language build-in, but you may overload methods on your own. Eg overload + operator that is decorated in python by __add__ method:

class YourMath(object):
    def __init__(self, param):
        self.param = param

    def __add__(self, x):
        return int(str(self.param) + str(x.param)) # concatenation 


x = YourMath(5)
y = YourMath(4)

+ will concatenate instead of sum up. Result of x+y in this case is 54.

edited Apr 06 '16 at 08:23

answered Apr 06 '16 at 08:12

Rudziankoŭ

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Is this an example of operator overloading as well: "import math as m"? – MmmHmm Apr 06 '16 at 19:35
No "import math as m" is import of `math` module with alias `m` – Rudziankoŭ Apr 07 '16 at 06:00

string formatting with modulus/percent sign

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