Relational Python: Displaying Relations

Here is the first pass of a method I wrote for displaying the relation in tabular form. One or two of the for loops could probably be replaced with a list comprehension and I should probably write to a file object that gets passed in rather than use print, but it serves the purpose of pretty printing during experimentation on the relational operators.

It will result in a display like:

    +-----+-------+-----+--------+
    | ENO | ENAME | DNO | SALARY |
    +-----+-------+-----+--------+
    | E1  | Lopez | D1  | 40K    |
    | E3  | Finzi | D2  | 30K    |
    | E2  | Cheng | D1  | 42K    |
    +-----+-------+-----+--------+

If it seems inefficient that display uses self.tuples() rather than self.tuples_, it is because that way it will work later on on views where tuples() is dynamic.

    def display(self):

        columns = range(len(self.attributes_))
        
        col_width = [len(self.attributes_[col]) for col in columns]

        for tupdict in self.tuples():
            tup = self._convert_dict(tupdict)
            for col in columns:
                col_width[col] = max(col_width[col], len(tup[col]))
        
        hline = ""
        for col in columns:
            hline += "+-" + ("-" * col_width[col]) + "-"
        hline += "+"

        def line(row):
            l = ""
            for col in columns:
                value = row[col]
                l += "| " + value + (" " * (col_width[col] - len(value))) + " "
            l += "|"
            return l
    
        print hline
        print line(self.attributes_)
        print hline

        for tup in self.tuples():
            print line(self._convert_dict(tup))

        print hline