Lecture 18, Thu 03/07

Recursion cont., File IO

Recorded Lecture: 3_7_24

Exploring All Possibilities with Recursion

• Walkthrough zyBooks 9.6.1

Files

• Files are a valuable tool to help us solve many other types of problems
• Files give us persistence
  • Our data can be saved between each program execution

File Basics

• We can read from files
• We can write to files
• We can store files in many different forms
  • Example: .xls, .docx, .pdf, .jpg
• On our computers, you can think of:
  • File: A document
  • Directory: A folder containing files and other folders
  • File System: Collection of all the files and folders on the computer

File I/O:

• I/O stands for Input / Output
• Steps for File I/O

1. Open the file (creates a connection between your program and the file)
   • Choose if the connection will be for reading, writing, or appending to a file
2. Read the data / write the data
3. Close the file (close the connection). This needs to be done once per opened file
   • Note that your code will probably run OK if you forget to close the file for small programs not dealing with a lot of file IO
   • However, your computer uses resources to keep track of all open files. Forgetting to close a file will be problematic if your program is performing a lot of file IO during runtime

Common Ways to Read Data From Files

• read() method – Reads the entire file into one string
• readline() method - Read everything from the current position to the next \n (or to the end of the file, EOF). If nothing left to read, returns an empty string.
• readlines() method - Read all the lines in the file into a list
• for loop - Read a line of text (separated by \n) each iteration
• Examples reading from file (example.txt) located in the same directory as our .py file:

This is Line 1
This is Line 2
This is Line 3

# Reading entire contents of file into program
infile = open('example.txt') 
data = infile.read()
print(data)
infile.close()