In order to read the file line by line, use readline().

Let's see the sample code readline1.py:

file_input = open("sample1.txt",'r')
print file_input.readline()
print file_input.readline()
print file_input.readline()
file_input.close()

Let's see the output of code:

In code, we have printed three lines. What happens, if you specify count in readline(count). See the code readlinecount.py:

file_input = open("sample1.txt",'r')
print  file_input.readline(100)
print  file_input.readline(20)
file_input.close()

 Let's see the output:

In the file_input.readline(100) syntax prints 100 characters of the first line. But the first line contains only 48 characters. The syntax file_input.readline(20) prints the 20 characters from the second line of sample1.txt.