CS 149
Professor: Alvin Chao
File I/O
Importing a Module
outfile = open("out.txt", "w")
outfile.write("Example ")
outfile.write("output ")
outfile.write("text file\n")
outfile.write("xyz Coordinates\n")
outfile.write("MODEL\n")
outfile.write(f"ATOM {1:3d}")
seq = f"n {0:5.1f}{1:5.1f}{2:5.1f}"
outfile.write(seq)
outfile.write("\n")
outfile.close()
out.txt��Example output text file
xyz Coordinates
MODEL
ATOM 1n 0.0 1.0 2.0
Questions
a) How many arguments are passed to open? What are their types?
b) What variable stores the file object returned by the open function?
c) Identify the names of all methods used on this file object in the code.
d) What type of data does the write method require for its argument?
out.txt
Based on the out.txt file:�a) How many times was the write method called to create the first line of text?
�b) How many times was the write method called to create the second line of text?
c) What does the "\n" character do when writing to the file?
d) How is the write method different from the print function?
What does this code do?
outfile = open("lines.txt", "w")
for i in range(1, 101):
outfile.write(f"Line #{i}\n")
outfile.close()
Append to a file
Python Code | Shell Ouput |
afile.write("new line\n") | NameError: name ’afile’ is not defined |
afile = open("out.txt", "a") | |
afile.write("new line\n") | 9 |
afile.write(2.0) | TypeError: write() argument must be str, not float |
afile.write("2.0") | 3 |
afile.close() | |
afile.write("new line\n") | ValueError: I/O operation on closed file. |
Read from a file
infile = open("out.txt", "r")�infile.readline()�infile.readline()�infile.readlines()�infile.readline()�infile.close()�infile = open("out.txt", "r")�for line in infile:� print(line)�infile.close()�infile = open("out.txt", "r")�for i in range(3):� infile.readline()�line = infile.readline()�infile.close()�line�line[0]�line[0:5]�words = line.split()�words�words[0]
Observations
What type does readline return? Readlines?
What is returned if you try to read past the end of the file?
What is the difference in the for loops?
File read
Write a program to read from a file called names.txt that has the first and last names of 5 presidents, one name per line (i.e. Abraham Lincoln) Write a program to list all the last names (second word of each line).
George Washington�Abraham Lincoln�Thomas Jefferson�James Madison�John Adams
PI Question
Copyright © 2023 C. Mayfield, T. Shepherd, and H. Hu. This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.
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