Unwanted output formatting when passing lists and strings

Question

I've been tasked to write a program in python to fit a given (and unchangeable) "driver" program which makes a Set class consisting of a single variable of a list called "members."

My problem is that output for the methods "has_subset()" and "intersect()" do not display properly. There are unnecessary parenthesis, commas, and apostrophes in the output.

Here is the set class:

class Set:
def __init__(self):
    self.members = []

def add_element(self, integer):
    if integer not in self.members:
        self.members.append(integer)

def remove_element(self, integer):
    while integer in self.members: self.members.remove(integer)

def remove_all(self):
    self.members = []

def has_element(self, x):
    while x in self.members: return True
    return False

# probably doesnt work, __repr__
def __repr__(self):
    if len(self.members) == 0:
        return "{}"
    return "{" + ", ".join(str(e) for e in self.members) + "}"

#Same as above, probably doesnt work
def __str__(self):
    if len(self.members) == 0:
        return "{}"
    return "{" + ", ".join(str(e) for e in self.members) + "}"

def __add__(self, other):
    counter = 0
    while counter < len(other.members):
        if other.members[counter] not in self.members:
            self.members.append(other.members[counter])
        counter = counter + 1
    return self.members

def intersect(self, x):
    counter = 0
    answer = Set()
    while counter < len(x.members):
        if x.members[counter] in self.members: answer.members.append(x.members[counter])
        counter = counter + 1
    return answer

#No clue if this is what is intended
def has_subset(self, x):
    counter = 0
    while counter < len(x.members):
        if x.members[counter] not in self.members: return False
        counter = counter + 1
    return True

Here is the driver file:

    from Set import *

first = Set()
count = 0
while count < 10:
    first.add_element(count)
    count += 1
print(first)

second = Set()
count = 5
while count < 15:
    second.add_element(count)
    count += 1
print(second)    

third = Set()
third.add_element(2)
third.add_element(1)
third.add_element(8)
third.add_element(5)

#Tests has_subset with a set that is a subset
if first.has_subset(third):
    print(third, "is a subset of", first)
else:
    print(third, "is not a subset of", first)

#Tests has_subset with a set that is not a subset
if second.has_subset(third):
    print(third, "is a subset of", second)
else:
    print(third, "is not a subset of", second)

#Tests overloaded +
fourth = first + second
print(first, "+", second, "=\n", fourth)

#Tests intersect
fifth = first.intersect(second)
print(fifth, "is the intersection of", first, "and\n", second)

And here is the output:

{0, 1, 2, 3, 4, 5, 6, 7, 8, 9}
{5, 6, 7, 8, 9, 10, 11, 12, 13, 14}
({2, 1, 8, 5}, 'is a subset of', {0, 1, 2, 3, 4, 5, 6, 7, 8, 9})
({2, 1, 8, 5}, 'is not a subset of', {5, 6, 7, 8, 9, 10, 11, 12, 13, 14})
({0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14}, '+', {5, 6, 7, 8, 9, 10, 11, 12, 13, 14}, '=\n', [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14])
({5, 6, 7, 8, 9, 10, 11, 12, 13, 14}, 'is the intersection of', {0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14}, 'and\n', {5, 6, 7, 8, 9, 10, 11, 12, 13, 14})

Notice how the first two lines are properly formatted with no parenthesis, but once additional strings are combined, the unwanted punctuation comes into play. How do I create output by only editing the Set class to remove this unwanted output?

Answer 1

This has nothing to do with your Set class -- the problem is with how you're printing your content.

I suspect you're using Python 2.x?

If so, when you do print(third, "is a subset of", second) , you're actually telling Python to print the tuple (which contains 3 elements). Python obliges, and prints the parens and commas since that's part of printing a tuple. print(...) isn't a function in Python 2.

To fix this, you can either manually add together each piece:

print str(third) + ' is a subset of ' + str(second)

...or use string formatting:

print '{} is a subset of {}'.format(third, second)

...or add the line from __future__ import print_function at the top of your driver file to include Python 3 printing semantics, which does turn print(...) into a function and does what you want.