CODEWITHSUNDEEP
pythonparameter-passing
Student
Student

Reputation: 28345

Passing 1 argument, and it's saying I'm passing 2

import os
import sys

class Corrector:

    def correctAll(dir):
        print "ok"

c = Corrector()
c.correctAll(os.getcwd())

This code is printing:

TypeError: correctAll() takes exactly 1 argument (2 given)

but AFAIK os.getcwd() returns a single string.. what's wrong here?

Upvotes: 0

Views: 109

Answers (4)

Ming-Tang
Ming-Tang

Reputation: 17651

Your correctAll is missing the self parameter: All instance methods must have self as its first argument, it means "the object itself" In other words, c.correctAll(x) is like Corrector.correctAll(c, x)

Python shell example

>>> class Test:
...   def doSomething(s, x): print x
... 
>>> Test().doSomething(1)
1
>>> Test.doSomething(Test(), 1)
1
>>> Test()
<__main__.Test instance at 0xb7793acc>
>>>

Working code:

import os
import sys

class Corrector:

    def correctAll(self, dir):
        print "ok"

c = Corrector()
c.correctAll(os.getcwd())

See also: http://docs.python.org/tutorial/classes.html

Upvotes: 1

Rudie
Rudie

Reputation: 53781

Shouldn't you define self in the argument list as well?

class Corrector:

    def correctAll(self, dir):
        print "ok"

Maybe I'm wrong...

Upvotes: 0

ThiefMaster
ThiefMaster

Reputation: 318488

In python you must accept the instance argument - called self - explicitely (while other languages simply provide it automagically). So your method definition must looks like def correctAll(self, dir).

Upvotes: 1

aaronasterling
aaronasterling

Reputation: 70994

You need to accept self as an argument or use the staticmethod decorator.

class Corrector:

    def correctAll(self, dir):
        print "ok"

or

class Corrector:

    @staticmethod
    def correctAll(dir):
        print "ok"

The distinction between the two is if you want the method to have access to the instance that it's called on or not. If so, then use the first one and the the instance will be available as self. Otherwise, you can use the second one.

Python methods work by explicitly accepting the object that they are bound to as their first argument (self is canonical here but it can really be anything). That argument is then implicitly passed when a call occurs.

Upvotes: 4

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