Locating File Positions in Python

Locating file positions in Python means identifying the current position of the file pointer within an open file. Python provides the tell() and seek() methods of the file object for this task.

Locating the File Position

The tell() method tells you the current position within the file. In other words, it specifies that the next read or write will occur at that many bytes from the beginning of the file.

Example

The following example shows how to get the current file position using the tell() method. Initially, when a file is opened, the pointer is placed at the beginning. After reading a specific number of characters, the file pointer moves forward by that number. The example below demonstrates the same.

# Create a file
data = """Python is a great language.
Yeah its great!!"""
with open("foo.txt", 'w') as f:
    f.write(data)

# Open the file 
fo = open("foo.txt", "r")

# Get current file position
position = fo.tell()
print("Current file position before Read():", position)

# Read first 5 characters
data = fo.read(5)
print("Read string is:", data)

# Get current file position
position2 = fo.tell()
print("Current file position after read():", position2)

# Close the file
fo.close()

Output of the above program is as follows ?

Current file position before Read(): 0
Read string is: Pytho
Current file position after read(): 5

Changing the File Position

The seek(offset[, whence]) method of the file object changes the current file position. The offset argument indicates the number of positions to be moved.

Example

This example demonstrates getting and changing the file position using the tell() and seek() methods.

# Create a file
data = """Python is a great language.
Yeah its great!!"""
with open("foo.txt", 'w') as f:
    f.write(data)

# Open the file
fo = open("foo.txt", "r+")

# Read first 4 characters
data = fo.read(4)
print("Read string is :", data)

# Check current position
position = fo.tell()
print("Current file position : ", position)

# Reposition pointer at the beginning once again
position = fo.seek(0, 0)
data = fo.read(10)
print("Read string again :", data)

# Again check current position
position2 = fo.tell()
print("Current file position : ", position2)

# Close opened file
fo.close()

This produces the following result ?

Read string is : Pyth
Current file position :  4
Read string again : Python is 
Current file position :  10