CODEWITHSUNDEEP
python
Miya Tseng-West
Miya Tseng-West

Reputation: 15

Opening file vs reading file in python

I am attempting to print the file, split by line using two methods: one is using the method read on files and the second is using a for loop and splitting the files into lines. I am getting a Traceback error on the last line stating that "words" is not defined. I cannot see why this is the case.

fname = input('enter file name')
try:
 fhandle = open(fname, 'r')
except:
 print('file does not exist')
 exit()
#store entire file in a variable called data
data = fhandle.read()
print(data)
#iterate through each line in a file handle
for line in fhandle:
 line = line.strip()
 words = line.split()

print(words)

Upvotes: 1

Views: 426

Answers (2)

Arifa Chan
Arifa Chan

Reputation: 1015

words it not define because of read(), it makes for loop didn't return anything.

Python file method read() reads at most size bytes from the file. If the read hits EOF before obtaining size bytes, then it reads only available bytes.

When print(words) is indented in for loop, it just return nothing too. But if read() is removed while print(words) isn't indented, it'll return a list of the last line:

fname = input('enter file name')
try:
    fhandle = open(fname, 'r')
except:
    print('file does not exist')
    exit()
# store entire file in a variable called data
# data = fhandle.read()
# print(data)
# iterate through each line in a file handle
for line in fhandle:
    line = line.strip()
    words = line.split()
print(words)

# ['Line', '4']

And if print(words) is indented while read() is removed, it'll return this:

fname = input('enter file name')
try:
    fhandle = open(fname, 'r')
except:
    print('file does not exist')
    exit()
# store entire file in a variable called data
# data = fhandle.read()
# print(data)    
# iterate through each line in a file handle
for line in fhandle:
    line = line.strip()
    words = line.split()
    print(words)

# ['Line', '1']
# ['Line', '2']
# ['Line', '3']
# ['Line', '4']

I'm not sure what is your intent using split() but if you just want to print line by line using read(), your code already did that.

When using for loop, just comment or remove read() then just print line

fname = input('enter file name')
try:
    fhandle = open(fname, 'r')
except:
    print('file does not exist')
    exit()
# store entire file in a variable called data
# data = fhandle.read()
# print(data)
# iterate through each line in a file handle
for line in fhandle:
    print(line.strip())

# Line 1
# Line 2
# Line 3
# Line 4

But if you're intend to make a list consisted of each line, you can use splitlines()

fname = input('enter file name')
try:
    fhandle = open(fname, 'r')
except:
    print('file does not exist')
    exit()
#store entire file in a variable called data
data = fhandle.read().splitlines()
print(data)

# ['Line 1', 'Line 2', 'Line 3', 'Line 4']

Hopes this help.

Upvotes: 0

Anonymous12358
Anonymous12358

Reputation: 489

When reading a file, Python keeps track of a cursor within the file. Data is read from the position of the cursor onwards, and reading moves the cursor forward to the end of the data that was read. This is so that, e.g., calling f.readline() twice will return the next line each time, rather than the first line both times.

When you call f.read(), the whole file is read, so the cursor is moved to the end of the file. Then, when you iterate through fhandle, Python only considers the lines ahead of the cursor — of which there are none. Since the object being iterated through is empty, the body of the for loop is never executed, so words is never assigned to.

You can fix this by calling fhandle.seek(0) directly before the for loop to return the cursor to the start of the file.

There is also a logical error in your program. If you want to print every line, not just the last, in your for loop, you need to indent print(words) so that it's in the for loop.

As a best practice, you should also call fhandle.close() when you're finished using the file.

Upvotes: 1

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