Asking questions and reading answers
Reading keyboard input
Reading from the command line
Providing input on the command line
A variable number of command-line arguments
More on command-line arguments
Turning user text into live objects
The magic eval function
The magic exec function
Turning string expressions into functions
Option-value pairs on the command line
Basic usage of the argparse module
Mathematical expressions as values
Reading data from file
Reading a file line by line
Alternative ways of reading a file
Reading a mixture of text and numbers
Writing data to file
Example: Writing a table to file
Standard input and output as file objects
What is a file, really?
Handling errors
Exception handling
Raising exceptions
A glimpse of graphical user interfaces
Making modules
Example: Interest on bank deposits
Collecting functions in a module file
Test block
Verification of the module code
Getting input data
Doc strings in modules
Using modules
Distributing modules
Making software available on the Internet
Making code for Python 2 and 3
Basic differences between Python 2 and 3
Turning Python 2 code into Python 3 code
Summary
Chapter topics
Example: Bisection root finding
Exercises
Exercise 1: Make an interactive program
Exercise 2: Read a number from the command line
Exercise 3: Read a number from a file
Exercise 4: Read and write several numbers from and to file
Exercise 5: Use exceptions to handle wrong input
Exercise 6: Read input from the keyboard
Exercise 7: Read input from the command line
Exercise 8: Try MSWord or LibreOffice to write a program
Exercise 9: Prompt the user for input to a formula
Exercise 10: Read parameters in a formula from the command line
Exercise 11: Use exceptions to handle wrong input
Exercise 12: Test validity of input data
Exercise 13: Raise an exception in case of wrong input
Exercise 14: Evaluate a formula for data in a file
Exercise 15: Write a function given its test function
Exercise 16: Compute the distance it takes to stop a car
Exercise 17: Look up calendar functionality
Exercise 18: Use the StringFunction tool
Exercise 19: Why we test for specific exception types
Exercise 20: Make a complete module
Exercise 21: Organize a previous program as a module
Exercise 22: Read options and values from the command line
Exercise 23: Check if mathematical identities hold
Exercise 24: Compute probabilities with the binomial distribution
Exercise 25: Compute probabilities with the Poisson distribution
References
Consider a program for evaluating the formula \( x = A\sin(w t) \):
from math import sin
A = 0.1
w = 1
t = 0.6
x = A*sin(w*t)
print x
A, w, and t are input data in the sense that these parameters
must be known before
the program can perform the calculation of x. The results
produced by the program, here x, constitute the output data.
Input data can be hardcoded in the program as we do above. That is, we
explicitly set variables to specific values: A=0.1, w=1, t=0.6.
This programming style may be suitable for small programs. In
general, however, it is considered good practice to let a user of the
program provide input data when the program is running. There is then
no need to modify the program itself when a new set of input data is
to be explored. This is an important feature, because
a golden rule of programming is that modification of
the source code always represents a danger of introducing new errors
by accident.
This document starts with describing four different ways of reading data into a program:
The Python programming environment is organized as a big collection of modules. Organizing your own Python software in terms of modules is therefore a natural and wise thing to do. The section Making modules tells you how easy it is to make your own modules.
All the program examples from the present document are available in files in the src/input folder.
This chapter is taken from the book A Primer on Scientific Programming with Python by H. P. Langtangen, 5th edition, Springer, 2016.