I have a question that spawned from writing my own class to manage a two-dimension table.
I started by creating a simple class as follows, creating an empty_line object that was copied as much as needed to create the number of lines:
class Table(object):
"""Table class, allows the creation of new lines and columns to the table"""
def __init__(self, col = 1, lines = 1, defaultcontent=''):
self.columns = col
self.lines = lines
self.empty_line = [defaultcontent for i in range(self.columns)]
self.table = [self.empty_line for j in range(self.lines)]
def add_line(self):
self.table.append(self.empty_line)
self.lines += 1
def add_column(self):
self.empty_line.append('')
for i in range(self.lines):
self.table[i].append('')
However, after I created a table, for example with table = Table(5,3), and do an assignment with table.table[1][2] = 'something', I realised the 'something' found itself in every line, and that I couldn't change a single line without having the others changed. Also, self.empty_line was changed.
After a little while, I wrapped my head around the problem being in the self.empty_line usage. I rewrote my class, this time taking out the self.empty_line and replacing it with the primitive ['' for i in range(self.columns)] (and of course also correcting the bug in the add_column() method that would add two columns instead of just one!).
My problem went away, but a question still lingers: Shouldn't the self.table = [self.empty_line for j in range(self.lines)] create a copy of the self.empty_line object for every new line, instead of somehow 'linking' the same self.empty_line instance (that gets changed).
So what am I doing wrong, and where is the hole in my knowledge about python objects?
