method within class is not callable within that class?

Question

If I have a file, foo.py with contents:

import pandas as pd

class Marcher(object):
    def __init__(self, p_path):
        self.p_path = p_path

    p_m = 'ID'

    def first_call(self):
        df_p = pd.read_csv(self.p_path, header=None)
        return df_p

    def p_to_i(self, p):
        pii = p.set_index(self.p_m, drop=False).loc[p[self.p_m]]
        return pii

    m1 = p_to_i(first_call())

What I would like to do with this is something like this:

test = Marcher(p_path='/some/path/to/file.csv')
test.m1

However when I try this I get back an error:

TypeError: first_call() takes exactly 1 argument (0 given)

Possible duplicate of [How to decorate a method inside a class?](http://stackoverflow.com/questions/1367514/how-to-decorate-a-method-inside-a-class) — Two-Bit Alchemist, Aug 29 '16 at 20:07

score 2 · Accepted Answer · answered Aug 29 '16 at 20:12

2

why do you want m1 to be a class member variable? just move the call like this:

def __init__(self, path):
    self.path = path
    self.m1 = self.p_to_i(self.first_call())

answered Aug 29 '16 at 20:12

acushner

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Bi Rico · Answer 2 · 2016-08-29T20:21:32.853

The issue is you're trying to call the methods before creating an instance. Take for instance a simple Circle class:

import math

class Circle(object):
    def __init__(self, radius):
        self.radius = radius
    def get_area(self):
        return math.pi * self.radius ** 2
    # You cannot do this because every circle can have a different radius
    # area = get_area()

    # But you can use a property
    @property
    def area(self):
        return self.get_area()

print Circle(2).area
# 12.5663706144
print Circle(10).area
# 314.159265359

Also, sometimes people like to cache property values to avoid re-computing them, that looks something like this:

class Circle(object):
    # ...
    _area = None
    @property area(self):
        if self._area is None:
            self._area = self.get_area()
        return self._area

The downside to this method is that Circle is no longer a dynamic object, you should not update the "radius" attribute once the instance is created because the area is cached and will not get updated.

method within class is not callable within that class?

2 Answers2