Index out of range in python while reading multiple lines from a file

Question

I am confused with indexing in python. I am using the following code to read a line from a file and print the first item in the list. I think that every time a line is read the index is set to zero. I am getting an index out of range for the following code. Please explain where I am going wrong.

fname = input("Enter file name: ") 

fh = open(fname)  
for line in fh:     
 line = line.strip()     
 print(line)      
 b = line.split()  
 print(b[0]) 

Answer 1

It can go bad if the string is empty.

In [1]: line = '     '
In [2]: line = line.strip()
In [4]: b = line.split()
In [5]: b
Out[5]: []
In [6]: b[0]
---------------------------------------------------------------------------
IndexError                                Traceback (most recent call last)
<ipython-input-6-422167f1cdee> in <module>()
----> 1 b[0]

IndexError: list index out of range

Perhaps update your code as follows:

fname = input("Enter file name: ") 

fh = open(fname)  
for line in fh:     
    line = line.strip()     
    b = line.split()
    if b: 
        print(b[0]) 

Answer 2

If line is blank (in other words it consists only of whitespace and a carriage return) then after line.strip() it will be the null string.

>>> line = ""
>>> line.split()[0]

Traceback (most recent call last):
  File "<pyshell#50>", line 1, in <module>
    line.split()[0]
IndexError: list index out of range

In other words, when you use split on the null string, you get an empty list back. So there is no element zero.

Answer 3

As explained previously, if line is blank, you will get an index error.

If you want to read lines, maybe change a little your code to let Python do the job for you

fname = input("Enter file name: ") 
with open(fname) as f
    lines = f.readlines()
# f will be closed at end of With statement no need to take care
for line in lines:     
    line = line.strip()     
    print(line)      
    # following line may not be used, as line is a String, just access as an array
    #b = line.split()
    print(line[0])