Wednesday, February 25, 2015

Publish SQLite data to PDF using named tuples

By Vasudev Ram

Some time ago I had written this post:

Publishing SQLite data to PDF is easy with xtopdf.

It showed how to get data from an SQLite (Wikipedia) database and write it to PDF, using xtopdf, my open source PDF creation library for Python.

Today I was browsing the Python standard library docs, and so thought of modifying that program to use the namedtuple data type from the collections module of Python, which is described as implementing "High-performance container datatypes". The collections module was introduced in Python 2.4.
Here is a modified version of that program,, called, that uses named tuples:
# Author: Vasudev Ram -
# is a program to demonstrate how to read 
# SQLite database data and convert it to PDF. It uses the Python
# data structure called namedtuple from the collections module of 
# the Python standard library.

from __future__ import print_function
import sys
from collections import namedtuple
import sqlite3
from PDFWriter import PDFWriter

# Helper function to output a string to both screen and PDF.
def print_and_write(pw, strng):


    # Create the stocks database.
    conn = sqlite3.connect('stocks.db')
    # Get a cursor to it.
    curs = conn.cursor()

    # Create the stocks table.
    curs.execute('''DROP TABLE IF EXISTS stocks''')
    curs.execute('''CREATE TABLE stocks
                 (date text, trans text, symbol text, qty real, price real)''')

    # Insert a few rows of data into the stocks table.
    curs.execute("INSERT INTO stocks VALUES ('2006-01-05', 'BUY', 'RHAT', 100, 25.1)")
    curs.execute("INSERT INTO stocks VALUES ('2007-02-06', 'SELL', 'ORCL', 200, 35.2)")
    curs.execute("INSERT INTO stocks VALUES ('2008-03-07', 'HOLD', 'IBM', 300, 45.3)")

    # Create a namedtuple to represent stock rows.
    StockRecord = namedtuple('StockRecord', 'date, trans, symbol, qty, price')

    # Run the query to get the stocks data.
    curs.execute("SELECT date, trans, symbol, qty, price FROM stocks")

    # Create a PDFWriter and set some of its fields.
    pw = PDFWriter("stocks.pdf")
    pw.setFont("Courier", 12)
    pw.setHeader("SQLite data to PDF with named tuples")
    pw.setFooter("Generated by xtopdf -")

    # Write header info.
    hdr_flds = [ str(hdr_fld).rjust(10) + " " for hdr_fld in StockRecord._fields ]
    hdr_fld_str = ''.join(hdr_flds)
    print_and_write(pw, '=' * len(hdr_fld_str))
    print_and_write(pw, hdr_fld_str)
    print_and_write(pw, '-' * len(hdr_fld_str))

    # Now loop over the fetched data and write it to PDF.
    # Map the StockRecord namedtuple's _make class method
    # (that creates a new instance) to all the rows fetched.
    for stock in map(StockRecord._make, curs.fetchall()):
        row = [ str(col).rjust(10) + " " for col in (, \
        stock.trans, stock.symbol, stock.qty, stock.price) ]
        # Above line can instead be written more simply as:
        # row = [ str(col).rjust(10) + " " for col in stock ]
        row_str = ''.join(row)
        print_and_write(pw, row_str)

    print_and_write(pw, '=' * len(hdr_fld_str))

except Exception as e:
    print("ERROR: Caught exception: " + e.message)


This time I've imported print_function so that I can use print as a function instead of as a statement.

Here's a screenshot of the PDF output in Foxit PDF Reader:

- Vasudev Ram - Online Python training and programming

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Anonymous said...

Why use """
BBB = [ FUNC(A) + " " for A in AAA ]
and then """
CCC = ''.join(BBB)

BBB = [ FUNC(A) for A in AAA ]
CCC = ' '.join(BBB)
does a better job as it does not add a final space.
And I think it is much clearer, but that's personal.

Vasudev Ram said...

Thanks for the comment.

You're right, the "plus space" is not needed, though not wrong.

I had actually used similar logic to yours in an earlier post:

I might have edited the code in the current post a bit, and missed that improvement in the process of doing so.