How does tell() in python file handling work - python-3.x

Question

f = open("test.txt","w")
s= "This\nThis\nThis"
f.write(s)
f.close()
f= open("test.txt","r")
w=''
for i in f:
for j in i:
w = w+j
print(w)
print("Number of Characters",len(w))
print("Current Position of handler",f.tell())
f.close()
The output of the above is
This
This
This
Number of Characters 14
Current Position of handler 16
As per the file, there are 12 characters and 2 escape sequences so the number of characters is 14. I got it. But I did not get why the tell() function returns 17

Answer 1

Just an assumption.
I think, in your case, just for '\n', the pointer is moving twice. First, after reading the newline character i.e. \n, the pointer is moving one step right. Secondly, because of newline character, the pointer is going to the beginning of the next line. That's why an extra count is being added to tell() function's result. This won't be happen for other escape characters like '\t' etc.
I ran some examples on my system. You can notice the results one by one.
Example 1
f = open("test.txt","w")
s= "\t"
f.write(s)
f.close()
f= open("test.txt","r")
w=''
for i in f:
for j in i:
w = w+j
print(w)
print("Number of Characters",len(w))
print("Current Position of handler",f.tell())
f.close()
Output
>>>python .\test.py
Number of Characters 1
Current Position of handler 1
Example 2
f = open("test.txt","w")
s= "\n"
f.write(s)
f.close()
f= open("test.txt","r")
w=''
for i in f:
for j in i:
w = w+j
print(w)
print("Number of Characters",len(w))
print("Current Position of handler",f.tell())
f.close()
Output
>>>python .\test.py
Number of Characters 1
Current Position of handler 2
Example 3
f = open("test.txt","w")
s= "ThisThisThis"
f.write(s)
f.close()
f= open("test.txt","r")
w=''
for i in f:
for j in i:
w = w+j
print(w)
print("Number of Characters",len(w))
print("Current Position of handler",f.tell())
f.close()
Output
>>>python .\test.py
ThisThisThis
Number of Characters 12
Current Position of handler 12
Example 4
f = open("test.txt","w")
s= "ThisThisThis\n"
f.write(s)
f.close()
f= open("test.txt","r")
w=''
for i in f:
for j in i:
w = w+j
print(w)
print("Number of Characters",len(w))
print("Current Position of handler",f.tell())
f.close()
Output
>>>python .\test.py
ThisThisThis
Number of Characters 13
Current Position of handler 14
Example 5
f = open("test.txt","w")
s= "ThisThisThis\t"
f.write(s)
f.close()
f= open("test.txt","r")
w=''
for i in f:
for j in i:
w = w+j
print(w)
print("Number of Characters",len(w))
print("Current Position of handler",f.tell())
f.close()
Output
>>>python .\test.py
ThisThisThis
Number of Characters 13
Current Position of handler 13
For your case, you used \n two times in your string. You can count 2 instead of 1 for every \n while guessing the result of tell(). So, 4 + 2 + 4 + 2 + 4 = 16.