14.6 Chapter summary

Highlights from this chapter include:

Python can read and write data in files using the built-in open() function.
Due to buffering, changes to a file may not be visible until the file is closed.
Newline characters need to be removed/added when reading/writing files.
Comma-separate-value (CSV) files are commonly used to represent data.
Exceptions that cause a program to terminate can be handled using try and except.
Raising an exception is an alternative way to return from a function when an error occurs.

**Table 14.3** Chapter 14 reference.
Statement	Description
`file = open("myfile.txt")`	Open a file for reading.
`file = open("myfile.txt", 'w')`	Open a file for writing.
`file = open("myfile.txt", 'a')`	Open a file for appending.
`file.close()`	Close a file after making changes.
`data = file.read()`	Read the entire contents of a file. The variable `data` is a string.
`data = file.readline()`	Read the next line of a file. The variable `data` is a string.
`data = file.readlines()`	Read all lines of a file. The variable `data` is a list of strings.
`file.write("Have a nice day!\n")`	Writes a line to a file. In contrast to `print()`, the `write()` function does not automatically append a newline.
`file.write(["Line 1\n", "Line 2\n"])`	Writes multiple lines to a file. As with `write()`, a newline is not automatically added at the end of each line.
`try: # Statements except: # Statements`	Try to run statements that might raise an error. If any error is raised, run other statements.
`try: # Statements except ValueError: # Statements`	Try to run statements that might raise a `ValueError`. If a `ValueError` is raised, run other statements.
`try: # Statements except ValueError as err: # Statements`	Try to run statements that might raise a `ValueError`. If a `ValueError` is raised, run other statements. The variable `err` contains more details about the `ValueError`.
`raise ValueError`	Raises a `ValueError` with no specific error message.
`raise ValueError("number is prime")`	Raises a `ValueError` with the message `"number is prime"`.

Adapted from Introduction to Python Programming by OpenStax (openstax.org), licensed under CC BY-NC-SA 4.0. Changes were made. License: CC-BY-NC-SA-4.0.