read / write to text file - doesn't work all the time?

[Patrick De]

I am not quite sure I understand this. I have code that enters in grades to a text file. Works great. Here is the code :

outFile = open ("grades.txt", "w")
grade = 0
grade = input("enter a grade (q to quit)")
while (grade != "q"):
    outFile.write(grade + "\n")
    grade = input("enter a grade (q to quit)")
outFile.close()

And then I have a set of code that reads from the text file

# need some counters
count = 0
total = 0
# open the text file
inFile = open("grades.txt", "r")
#set grade to be the variable for each line read
grade = inFile.readline()
# introduce the while loop
while (grade):
    print (grade)
    # count to the next grade
    count += 1
    #totalling for average
    total = total + int(grade)
    # reading it
    grade = inFile.readline()
# working out the average and printing it
average = total / count
print ("Average : ", str(average))
inFile.close()

This all works great. Python enters the values into the textfile and I can read them using the code.
Then I try this :
-I manually go into the TEXT FILE and add a set of numbers - appending the ones I already have.
-After I do that, I get an error (below).
-Nothing else in my READ of the text file code has changed, just inputting the numbers manually.

Here is the error

Traceback (most recent call last):
  File "C:/Users/davids home/PycharmProjects/02Strings/06. while loops read all.py", line 14, in <module>

    total = total + int(grade)
20
ValueError: invalid literal for int() with base 10: '\n'

Any ideas?

[Paul Clapham]

If I understand right: the file generated by Code Fragment 1 can be read into Code Fragment 2 successfully, but if you manually edit that file then it can't be read into Code Fragment 2 successfully?

If so then the conclusion must surely be that your edits are the problem. So have a look at the "before" version -- the one which works -- and compare it to the "after" version, which doesn't work. Try to see what's different. If you don't see any difference then post the two versions and let another set of eyes do the looking.

[Patrick De]

I think I found the solution - although my assumption might not be correct, it seems to work. When the WRITE program finishes, it closes the file with inFile.close().
My guess is when I edit the file using Notepad, it does not close the file properly. I added this :

inFile = open("grades.txt")
inFile.close()

At the beginning of the program and now it works fine. Might be a poor solution, it might be windows things or a python thing.

Here is the full code

inFile = open("grades.txt")
inFile.close()
count = 0
total = 0
inFile = open("grades.txt", "r")
grade = inFile.readline()
while (grade):
    print (grade)
    count += 1
    total = total + int(grade)

    grade = inFile.readline()
average = total / count
print ("Average : ", str(average))

[Karthik Shiraly]

The problem with f.readline() is that it retains the newline character in return value.
You get that error if your file has empty lines and f.readline() returns just "\n". int() doesn't know what to do with a "\n".

A more pythonic way of doing this:
# 'with' automatically closes a file (or any closeable resource) when end of with block is reached.... with open('grades.txt', 'r') as f: # For each line in f.readlines(), if line.strip() is not a blank line, convert line to integer. # Return all such converted lines as a new list. This construct is called "list comprehensions" in python. grades = [int(line.strip()) for line in f.readlines() if line.strip()] # Use sum() and len() built-ins print "Average: ", sum(grades)/len(grades)