CODEWITHSUNDEEP
pythonoop
Ben Cooper
Ben Cooper

Reputation: 1495

Should I ever directly call object.__str__()?

I'm writing a class in Python and I'm writing a __str__() function so my print statements can print string representations of instances of that class. Is there ever a reason to directly do something like this:

myObj = Foo(params)
doSomething(myObj.__str__())

It feels like since there are other neater ways to do this, it would be a bad idea (or at least, not proper style) to directly call __str__(). That said, I can't find a website specifically saying not to.

Upvotes: 7

Views: 1825

Answers (3)

chepner
chepner

Reputation: 531798

In general, dunder methods define how an object behaves in a particular context. They aren't intended to be used directly. (The major exception being when you are overriding a dunder method inherited from a parent class.)

In the case of __str__, there are three documented uses; it is used by the built-in functions str, format, and print so that (roughly speaking)

  1. str(myObj) == myObj.__str__()
  2. format("{}", myObj) == format("{}", myObj.__str__())
  3. print(myObj) == print(myObj.__str__()).

The key here is that __str__ allows code that isn't built-in to Python to work with these functions; the __str__ method provides the common interface all three can use.

Upvotes: 5

Jean-François Fabre
Jean-François Fabre

Reputation: 140256

myObj.__str__()

is the same as

str(myObj)

unless someone has the bad idea to hide str built-in by reassigning its name:

str = lambda x: None

in which case only the first approach would work. But in the general case, it's better to avoid calling those dunder methods directly.

Upvotes: 3

Jean Rostan
Jean Rostan

Reputation: 1156

If you want a custom string representation of your class, implement __str__ in your class definition, and then you can call it using str(myObj) which will call your method. Calling __str__ will be the same, but isn't as clean I'd say.

Upvotes: 0

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