Python File Handling ( UNIT – V )
UNIT – v
Python
Programming - Python File Handling
1.
Introduction
- File handling in Python allows programs
to store data permanently on disk.
- Files are used to read
and write data for future use.
- Python provides built-in
functions such as open(), read(), write(), close() etc., for file operations.
2. Types
of Files in Python
Python
mainly works with two types of files:
|
Type |
Description |
Example |
|
Text
Files (.txt) |
Store
data as readable text (characters). Each line ends with a newline character \n. |
student.txt, notes.txt |
|
Binary
Files (.bin) |
Store
data in binary (0s and 1s). Used for images, audio, video, etc. |
image.jpg, data.bin |
3.
Opening a File
Files are
opened using the open() function.
Syntax:
file_object = open(filename, mode)
Common
File Modes:
|
Mode |
Description |
|
'r' |
Read
mode (default). File must exist. |
|
'w' |
Write
mode. Creates new file or overwrites existing one. |
|
'a' |
Append
mode. Adds data at end of file. |
|
'r+' |
Read
and write mode. |
|
'w+' |
Write
and read mode (overwrites file). |
|
'a+' |
Append
and read mode. |
|
'rb', 'wb', 'ab' |
Binary
file modes. |
Example:
f = open("data.txt", "r")
4.
Closing a File
After
completing operations, always close the file to free system resources.
Syntax:
f.close()
Example:
f = open("data.txt", "r")
content = f.read()
f.close()
Always
use close() after file operations or use a with
statement (auto-closes the file):
with open("data.txt", "r") as
f:
data =
f.read()
5.
Reading from a File
Python
provides multiple ways to read data:
|
Method |
Description |
Example |
|
read() |
Reads
entire file as a single string |
f.read() |
|
read(n) |
Reads
first n characters |
f.read(10) |
|
readline() |
Reads
one line at a time |
f.readline() |
|
readlines() |
Reads
all lines and returns a list |
f.readlines() |
Example:
f = open("data.txt", "r")
print(f.read()) # Read entire file
f.close()
6.
Writing to a File
(a)
write() method
- Writes a single string to a
file.
- Overwrites existing content
if file is opened in 'w'
mode.
Example:
f = open("sample.txt", "w")
f.write("Hello Students!\n")
f.write("Welcome to Python File
Handling.")
f.close()
Output
(in file):
Hello Students!
Welcome to Python File Handling.
(b)
writelines() method
- Writes multiple lines at
once using a list of strings.
- Each string must include \n for newlines.
Example:
f = open("student.txt", "w")
lines = ["Arun\n", "Bala\n",
"Charan\n"]
f.writelines(lines)
f.close()
Output
(in file):
Arun
Bala
Charan
7.
Reading and Writing Together
You can
open a file in read and write mode using 'r+', 'w+', or 'a+'.
Example:
f = open("demo.txt", "w+")
f.write("Python is fun!")
f.seek(0)
# Move cursor to beginning
print(f.read())
# Read what was written
f.close()
8. File
Handling with with Statement
The with keyword automatically closes the file after
operations.
Example:
with open("info.txt", "a") as
f:
f.write("New data added!\n")
No need
to call f.close() manually.
9. Common
File Methods
|
Method |
Description |
|
f.read() |
Reads
data |
|
f.readline() |
Reads
one line |
|
f.readlines() |
Reads
all lines into list |
|
f.write() |
Writes
a string |
|
f.writelines() |
Writes
multiple strings |
|
f.tell() |
Returns
current cursor position |
|
f.seek(pos) |
Moves
file cursor to position |
|
f.close() |
Closes
the file |
10.
Summary (Key Points for Exam)
- Python uses open() to open a file and close() to close it.
- File modes: 'r', 'w', 'a', 'r+', 'w+', 'a+'.
- Text files store readable
data; binary files store raw data.
- write() writes strings; writelines() writes multiple lines.
- Always use the with statement for automatic
file closing.
- Common operations: reading,
writing, appending, and deleting files.
File
Handling Methods in Python
1.
Introduction
Python
provides several built-in file handling methods for creating, reading,
writing, appending, and managing files.
The open() function is used to open files,
and file methods are used to perform operations such as reading,
writing, and moving within the file.
2.
append() Method
- The append() method is used with file
objects opened in 'a'
(append) or 'a+' mode.
- It adds data to the end
of an existing file without erasing previous contents.
- If the file does not exist,
Python will create a new file automatically.
Syntax:
file_object = open("filename.txt",
"a")
file_object.write("New line added.\n")
file_object.close()
Example:
f = open("notes.txt", "a")
f.write("This line is added later.\n")
f.close()
Appends
new data at the end of notes.txt.
3. read()
Method
- The read() method reads the entire
content of the file as a single string.
- You can also specify the number
of characters to read.
Syntax:
file_object.read(size)
Example:
f = open("data.txt", "r")
content = f.read()
print(content)
f.close()
Example
with Size:
f = open("data.txt", "r")
print(f.read(10))
# Reads first 10 characters
f.close()
4.
readlines() Method
- The readlines() method reads all lines
in a file and returns them as a list of strings.
- Each line in the list ends
with a newline character \n.
Example:
f = open("students.txt", "r")
lines = f.readlines()
print(lines)
f.close()
Output:
['Arun\n', 'Bala\n', 'Charan\n']
You can
also loop through lines:
for line in lines:
print(line.strip()) # Removes
newline
5. with
Keyword
- The with keyword is used for automatic
file handling.
- It ensures the file is closed
automatically after the block of code, even if an error occurs.
Syntax:
with open("file.txt", "r") as
f:
data =
f.read()
print(data)
No need
to call f.close().
Advantages:
- Cleaner code
- Automatic resource
management
- Prevents file corruption due
to unclosed files
6.
Splitting Words from a File
To split
file content into individual words, use the split() method.
Example:
with open("para.txt", "r") as
f:
data =
f.read()
words =
data.split() # splits by spaces
print(words)
Output:
['Python', 'is', 'a', 'powerful', 'language']
Note:
split('\n') can be used to split by lines,
and split(',') by commas.
7. File
Methods
|
Method |
Description |
Example |
|
read() |
Reads
all data |
f.read() |
|
readline() |
Reads
one line |
f.readline() |
|
readlines() |
Reads
all lines into a list |
f.readlines() |
|
write() |
Writes
a single string |
f.write("Hello") |
|
writelines() |
Writes
multiple strings |
f.writelines(list) |
|
seek(pos) |
Moves
cursor to a specific position |
f.seek(0) |
|
tell() |
Returns
current cursor position |
f.tell() |
|
close() |
Closes
the file |
f.close() |
8. File
Positions (seek() and tell())
(a)
tell()
- Returns the current
position of the file cursor (in bytes).
Example:
f = open("data.txt", "r")
print(f.tell())
# Output: 0
f.read(5)
print(f.tell())
# Output: 5
f.close()
(b)
seek()
- Used to move the file
cursor to a specific position.
Syntax:
f.seek(offset, from_what)
- offset: Number of bytes to move.
- from_what: 0 (beginning), 1
(current), 2 (end).
Example:
f = open("data.txt", "r")
f.seek(0) #
Move to beginning
data = f.read(10)
f.close()
9.
Renaming and Deleting Files
These
operations are performed using the os module.
(a)
Renaming a File
import os
os.rename("oldname.txt",
"newname.txt")
Changes
the file name.
(b)
Deleting a File
import os
os.remove("unwanted.txt")
Deletes
the specified file.
Note: Before deleting, always check if
the file exists using os.path.exists().
Example:
import os
if os.path.exists("sample.txt"):
os.remove("sample.txt")
else:
print("File not found!")
10.
Summary (Key Points for Exam)
- append() adds content at the end
of the file.
- read() reads entire file, readlines() reads all lines into
a list.
- with keyword handles automatic
closing of files.
- File positions managed by seek() and tell().
- Use os.rename() to
rename and os.remove() to delete files.
- Always close files after use
(or use with).
- split() method can be used to
separate words from file content.
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