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.

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".

Table 14.3 Chapter 14 reference.