files. - gramercydataappending data to an existing file dumas2.txt assignment: writing numeric data...
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AgendaThree Steps to Working With Files:
1. Open the file for reading or writing (appending).2. Read / Write.3. Close.
Three File Access Methods:
1. ‘r’ - Open a file for Reading only.2. ‘w’ - Writing. If the file already exist, erase it.
Create if it does not exist. 3. ‘a’ - Append to the end of the file. If it does not
exist, create it.
Specifying the location of a file.1. The file is created in the same folder as the script:
test_file = open (‘test.txt’, ‘w’)
2. You can specify a path as well as a filename. Use raw string to read the backslash characters as literal backslashes.
test_file = open (r‘C:\Users\Blake\Proj\test.txt’, ‘w’)
Writing data to a file
dumas.txt
Reading data from a file
Program output
Read one line at a time
Program output includes an extra blank line.readline() returns a string that ends with ‘\n’.
Concatenating a newline to a stringThis program writes three lines of text from three strings.
dumas2.txt
Appending data to an existing file
dumas2.txt
Assignment: writing numeric data
Solution
Reading numeric data: program output
Reading numeric data
6.2 Using Loops to Process Files
Program write_sales.py
Program output
sales.txt
Program: read_sales.py
sales.txt
Program output
the readline() method returns an empty string ‘’ when it has attempted to read beyond the end of a file. This makes it possible to write a while loop that determines when the end of a file has been reached.
Version 2 of the same program: read_sales2.pyThis for loop automatically reads line in a file without testing for any special condition that signals the end of the file.
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