CODEWITHSUNDEEP
pythonwxpython
nist
nist

Reputation: 1721

Strange extra argument

I got the following python code where printSaved is called when a button is clicked (using the wx library and python 2.7.2). But when this happens i got a really strange error

Traceback (most recent call last):
  File "./program.py", line 135, in printSaved
    s = self.readSaved()
TypeError: readSaved() takes no arguments (1 given)

Here is the code

  def readSaved():
    f = codecs.open((os.getenv('HOME') +'/Dokument/savefile.txt') ,'r','utf-8')
    l = f.readlines()
    f.close()
    return l

  def printSaved(self,event):
    s = self.readSaved()
    for l in s:
      print l

I fixed the problem by adding one argument to readSaved(somethingUseless) and everything worked fine. My question is what is passed to readSaved and HOW/WHY? Does this have something to do with the event?

Upvotes: 1

Views: 92

Answers (4)

StefanoP
StefanoP

Reputation: 3898

Is it defined within a class? I suppose it does, since the second method takes self.

If readSaved is an instance method, it takes self as first parameter as well. If you don't need it, use the @staticmethod decorator instead:

@staticmethod
def readSaved():
  f = codecs.open((os.getenv('HOME') +'/Dokument/savefile.txt') ,'r','utf-8')
  l = f.readlines()
  f.close()
  return l

Upvotes: 1

Ernest Friedman-Hill
Ernest Friedman-Hill

Reputation: 81724

As it is a method -- you're calling it as a method, anyway -- you have to have at least self as an argument. When a function is called as a method, the object you call the method through is passed as the first argument to that function.

Upvotes: 0

Platinum Azure
Platinum Azure

Reputation: 46233

In Python, the object on which a method is called is always passed in explicitly as an argument. This argument is conventionally called self.

The correct definition for readSaved() as an instance method should have this as the first line:

def readSaved(self):
    # ...

If you want it to be a module-level function, you should call it as follows:

s = readSaved()

Upvotes: 3

Ignacio Vazquez-Abrams
Ignacio Vazquez-Abrams

Reputation: 799460

Methods are passed the instance as the first argument.

Upvotes: 2

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