Retrieving data from a class without the str method

Question

I posses a class called Collatz and a function collatz_it which creates an object of the class, I'm trying to generate the number of steps for a number to reach 1 using the collatz conjucture and their corresponding steps till 1 million using a generator

import collatz
values = {}
count = 0
#collatz.collatz_it(n)

def gen():
    n = 0
    x = 0
    while True:
        yield x
        n += 1
        x = collatz.collatz_it(n)

for i in gen():
    count += 1
    values[count] = i
    print values
    if count == 1000000:
        break

As you can see, I generate the amount of steps taken for it to reach 1 using the collatz conjecture for a number given and add it to a dictionary with the corresponding number but when I print out the dictionary values, it's output is awkwardly something like this:

{1: 0}
{1: 0, 2: <collatz.Collatz instance at 0x01DCA580>}
{1: 0, 2: <collatz.Collatz instance at 0x01DCA580>, 3: <collatz.Collatz instance at 0x01DCDF58>}
{1: 0, 2: <collatz.Collatz instance at 0x01DCA580>, 3: <collatz.Collatz instance at 0x01DCDF58>, 4: <collatz.Collatz instance at 0x01DCDFA8>}
{1: 0, 2: <collatz.Collatz instance at 0x01DCA580>, 3: <collatz.Collatz instance at 0x01DCDF58>, 4: <collatz.Collatz instance at 0x01DCDFA8>, 5: <collatz.Collatz instance at 0x01DCDEB8>}
{1: 0, 2: <collatz.Collatz instance at 0x01DCA580>, 3: <collatz.Collatz instance at 0x01DCDF58>, 4: <collatz.Collatz instance at 0x01DCDFA8>, 5: <collatz.Collatz instance at 0x01DCDEB8>, 6: <collatz.Collatz instance at 0x01DCDE90>}
{1: 0, 2: <collatz.Collatz instance at 0x01DCA580>, 3: <collatz.Collatz instance at 0x01DCDF58>, 4: <collatz.Collatz instance at 0x01DCDFA8>, 5: <collatz.Collatz instance at 0x01DCDEB8>, 6: <collatz.Collatz instance at 0x01DCDE90>, 7: <collatz.Collatz instance at 0x01DE8940>}

If I print print i instead of print values I get the required output, this is basically because the print statement triggers the __str__ method in the class

Isn't there any way I could add the actual steps to the dictionary without entering <collatz.Collatz instance at 0x01DCDFA8> , Is there any sort of method of retrieving data as from a __str__ method so that my dictionary looks something like this:

{1: 0}
{1: 0, 2: 1}
{1: 0, 2: 1, 3: 7}

Answer 1

The default representation of any Python container is to use the repr() output of the contents, not str() .

The solution would be for you to either give the collatz.Collatz() instance a __repr__ method (you can monkey-patch that in), or to use a subclass of dict that uses str() instead of repr() when displaying the contents.

Monkey-patching in a __repr__ could be as simple as:

collatz.Collatz.__repr__ = collatz.Collatz.__str__

Of course, if this is your own code, just define a __repr__ method in the class body itself.

Answer 2

使用一个继承自dict的类，并拥有自己的__repr__ ，它__repr__您的需要。

Answer 3

Store the value that you want on this line:

values[count] = i

Do something like

values[count] = i.value

or

values[count] = str(i)

In the last case this assumed that you have written a __str__ method for the class:

class Collatz:
...
def __str__(self):
    return str(self.value)