Python module to facilitate reading input files. Downloads are available at PyPI or with 'pip' or 'easy_install'.
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A python module to facilitate reading input files

input_reader is used to define and read a general input file for a program. This README only contains a brief synopsis of what input_reader can do. For a more detailed description of the API, please see the documentation at The API is inspired by that of the argparse module from the python standard library, so hopefully it will be easy to learn.

The Problem

Let's say you have to write a program that cooks a meal. You have the following requirements:

  1. The user must specify one and only one of breakfast, lunch, or dinner.

    1. For breakfast, the user must specify scrambled or poached eggs and how many eggs. Also, the user specifies waffles or pancakes, and specifies if they want butter and/or syrup. The user may optionally request bacon.
    2. For lunch, the user must specify if they want a sandwich (BLT, ham, or turkey) or soup (vegetable or chili). The user also specifies if they want bread.
    3. For dinner, the user specifies steak (rare, medium or well), salmon, or pasta (red or white sauce). There is a choice of soup or salad. The user may also choose to have dessert.
  2. The user must specify a drink, and that drink can be water, milk, OJ, beer, soda, or wine.

  3. The user can request an organic meal and/or gluten-free.

How We Want the Input Files

Let's say that someone wants a scrambled egg breakfast with syrupy pancakes and bacon, and OJ for a drink. Here is how we might define the input:

drink oj

    eggs 2 scrambled
    pancakes syrup

Or, what if someone with a gluten allergy wants dinner with wine. They want a medium steak with salad, and they want the dessert. Here is the input:


drink wine

    steak medium

The input_reader Code

To define the above requirements, we would use the following code:

import sys
from input_reader import InputReader, ReaderError

reader = InputReader()

# Gluten free or organic meal?  These are simple booleans

# The drink has an argument, and accepts a specific list of values
reader.add_line_key('drink', type=('water', 'milk', 'oj', 'beer', 'soda', 'wine'))

# We are allowed to specify breakfast, lunch or dinner, so we use
# a mutually exclusive group.  We need one of these, so we call this
# required.
meal = reader.add_mutually_exclusive_group(required=True)

# We define the breakfast block
bfast = meal.add_block_key('breakfast')
# Eggs, number of eggs then the style
bfast.add_line_key('eggs', type=[int, ('scrambled', 'poached')], required=True)
# Pancakes OR waffles.  Syrup and/or butter is optional
wp = bfast.add_mutually_exclusive_group(required=True)
wp.add_line_key('waffles', type=None, glob={'len':'*', 'type':('syrup', 'butter')})
wp.add_line_key('pancakes', type=None, glob={'len':'*', 'type':('syrup', 'butter')})

# The lunch block
lunch = meal.add_block_key('lunch')
# Bread?
# Sandwitch or soup
ss = lunch.add_mutually_exclusive_group(required=True)
ss.add_line_key('sandwich', type=('blt', 'ham', 'turkey'))
ss.add_line_key('soup', type=('vegetable', 'chili'))

# The dinner block
dinner = meal.add_block_key('dinner')
# Dessert?
# Soup or salad?
ss = dinner.add_mutually_exclusive_group()
# Main course
mcourse = dinner.add_mutually_exclusive_group(required=True)
mcourse.add_line_key('steak', type=('rare', 'medium', 'well'))
mcourse.add_line_key('pasta', type=('red', 'white'))

You can read in and analyze the file in a manner given below:

# Assuming the input file is in argv[1], read in the input file
    inp = reader.read_input(sys.argv[1])
except ReaderError as e:

# Is the meal gluten free?
if inp.nogluten:

# Is lunch served?
if inp.lunch:
    # If so, what type of soup?
    if inp.lunch.soup == 'chili':

# Etc...


Seth M. Morton


03-01-2014 v. 1.2.2

  • Cleaned up import blocks
  • Added spaces between defs/classes (cosmetic)

01-29-2014 v. 1.2.1a

  • Fixed bug where strings were compared to unicode instead of basestring in python2.x

01-26-2014 v. 1.2.1

  • All calls are completely python2/3 compatible
  • Python2 uses unicode literals
  • Files use unicode encoding

01-16-2014 v. 1.2.0

  • Added input_reader.h to provide easy C interface to this python module
  • Added include_path attribute to input_reader module for C compilations
  • Removed (cause install problems for some)
  • Unit tests pass for both Python 2.7 and Python 3.x
  • Updated documentation

04-13-2013 v. 1.1.1

  • Added the filename attribute to the InputReader class

01-25-2013 v. 1.1.0

  • Increased code coverage of tests to ~98%
  • Refactored code to reduce copy/paste and be open for future improvements

01-14-2013 v. 1.0.2

  • Added input_file attribute to InputReader class
  • Fixed typo in documentation
  • Updated version updating code

12-22-2012 v. 1.0.1

  • Fixed error in

12-16-2012 v. 1.0.0

  • Fixed bugs in unit tests
  • Finished documentation with doctests
  • Added a post_process method to InputReader that can be subclassed
  • Made improvements to the setup process

12-3-2012 v. 0.9.1

  • Added unit tests
  • Added extra checks for bad input