File handling4.pdf

Computer Science
Class XII ( As per
CBSE Board)
Chapter 4
File Handling
Visit : python.mykvs.in for regular updates
New
syllabus
2023-24

Need for
a data file
• To Store data in organized manner
• To store data permanently
• To access data faster
• To Search data faster
• To easily modify data later on

File Handling
A file is a sequence of bytes on the disk/permanent storage where a group
of related data is stored. File is created for permanent storage of data.
In programming, Sometimes, it is not enough to only display the data on the
console. Those data are to be retrieved later on,then the concept of file
handling comes. It is impossible to recover the programmatically generated
data again and again. However, if we need to do so, we may store it onto
the file system which is not volatile and can be accessed every time. Here,
comes the need of file handling in Python.
File handling in Python enables us to create, update, read, and delete the
files stored on the file system through our python program. The following
operations can be performed on a file.
In Python, File Handling consists of following three steps:
➢ Open the file.
➢ Process file i.e perform read or write operation.
➢ Close the file.

File Handling
Types of File
There are two types of files:
Text Files- A file whose contents can be viewed using a text editor is called a text file. A text
file is simply a sequence of ASCII or Unicode characters. Python programs, contents written
in text editors are some of the example of text files.e.g. .txt,.rtf,.csv etc.
Binary Files-A binary file stores the data in the same way as as stored in the memory. The
.exe files,mp3 file, image files, word documents are some of the examples of binary files.we
can’t read a binary file using a text editor.e.g. .bmp,.cdr etc.
Text File Binary File
Its Bits represent character. Its Bits represent a custom data.
Less prone to get corrupt as change reflects as
soon as made and can be undone.
Can easily get corrupted, corrupt on even single
bit change
Store only plain text in a file.
Can store different types of data (audio,
text,image) in a single file.
Widely used file format and can be opened in any
text editor.
Developed for an application and can be opened
in that application only.
Mostly .txt,.rtf are used as extensions to text files. Can have any application defined extension.

File Handling
Opening and Closing Files-
To perform file operation ,it must be opened first then after reading
,writing, editing operation can be performed. To create any new file
then too it must be opened. On opening of any file ,a file relevant
structure is created in memory as well as memory space is created to
store contents.
Once we are done working with the file, we should close the file.
Closing a file releases valuable system resources. In case we forgot to
close the file, Python automatically close the file when program ends
or file object is no longer referenced in the program. However, if our
program is large and we are reading or writing multiple files that can
take significant amount of resource on the system. If we keep opening
new files carelessly, we could run out of resources. So be a good
programmer , close the file as soon as all task are done with it.

File Handling
open Function-
Before any reading or writing operation of any file,it must be
opened first
of all.Python provide built in function open() for it.On calling of
this function creates file object for file operations.
Syntax
file object = open(<file_name>, <access_mode>,< buffering>)
file_name = name of the file ,enclosed in double quotes.
access_mode= Determines the what kind of operations can be
performed with file,like read,write etc.
Buffering = for no buffering set it to 0.for line buffering set it to
1.if it is greater than 1 ,then it is buffer size.if it is negative then
buffer size is system default.

File Handling
File opening modes-
Sr.
No.
Mode & Description
1 r - reading only.Sets file pointer at beginning of the file . This is the default mode.
2 rb – same as r mode but with binary file
3 r+ - both reading and writing. The file pointer placed at the beginning of the file.
4 rb+ - same as r+ mode but with binary file
5 w - writing only. Overwrites the file if the file exists. If not, creates a new file for writing.
6 wb – same as w mode but with binary file.
7 w+ - both writing and reading. Overwrites . If no file exist, creates a new file for R & W.
8 wb+ - same as w+ mode but with binary file.
9 a -for appending. Move file pointer at end of the file.Creates new file for writing,if not exist.
10 ab – same as a but with binary file.
11 a+ - for both appending and reading. Move file pointer at end. If the file does not exist, it creates a new
file for reading and writing.
12 ab+ - same as a+ mode but with binary mode.

File Handling
Basic Text file operations
• Open (filename – absolute or relative path,
mode)
• Close a text file
• Reading/Writing data
• Manipulation of data
• Appending data into a text file

File Handling
Methods of os module
Before Starting file operation following methods must be learn by a programmer
to perform file system related methods available in os module(standard module)
which can be used during file operations.
1. The rename() method used to rename the file.
Syntax os.rename(current_file_name, new_file_name)
2. The remove() method to delete file.
Syntax os.remove(file_name)
3.The mkdir() method of the os module to create
directories in the current directory.
Syntax os.mkdir("newdir")
4.The chdir() method to change the current directory.
Syntax os.chdir("newdir")
5.The getcwd() method displays the current directory.
Syntax os.getcwd()
6. The rmdir() method deletes the directory.
Syntax os.rmdir('dirname')
e.g.program
import os
print(os.getcwd())
os.mkdir("newdir")
os.chdir("newdir")
print(os.getcwd())

File Handling
Absolute Path vs Relative Path
One must be familiar with absolute & relative path before starting file related operations.
The absolute path is the full path to some place on your computer. The relative path is the path
to some file with respect to your current working directory (PWD). For example:
Absolute path: C:/users/admin/docs/staff.txt
If PWD is C:/users/admin/, then the relative path to staff.txt would be: docs/staff.txt
Note, PWD + relative path = absolute path.
Cool, awesome. Now, if we write some scripts which check if a file exists.
os.chdir("C:/users/admin/docs")
os.path.exists("staff.txt")
This returns TRUE if stuff.txt exists and it works.
Now, instead if we write,
os.path.exists("C:/users/admin/docs/staff.txt")
This will returns TRUE.
If we don't know where the user executing
the script from, it is best to compute the absolute
path on the user's system using os and __file__.
__file__ is a global variable set on every Python
script that returns the relative path to the *.py file
that contains it.
e.g.program
import os
print(os.getcwd())
os.mkdir("newdir1")
os.chdir("newdir1")
print(os.getcwd())
my_absolute_dirpath =
os.path.abspath(os.path.dirname(__file__))
print(my_absolute_dirpath)

File Handling
File object attributes /
1. open a text file
➢ closed: It returns true if the file is closed and false when the file is open.
➢ encoding: Encoding used for byte string conversion.
➢ mode: Returns file opening mode
➢ name: Returns the name of the file which file object holds.
➢ newlines: Returns “r”, “n”, “rn”, None or a tuple containing all the newline
types seen.
E.g. Program
f = open("a.txt", 'a+') #1 open text file
print(f.closed)
print(f.encoding)
print(f.mode)
print(f.newlines)
print(f.name)
OUTPUT
False
cp1252
a+
None
a.txt

File Handling
2. Close a text file
close(): Used to close an open file. After using this method,an opened
file will be closed and a closed file cannot be read or written any more.
E.g. program
f = open("a.txt", 'a+')
print(f.closed)
print("Name of the file is",f.name)
f.close() #2 close text file
print(f.closed)
OUTPUT
False
Name of the file is a.txt
True

File Handling
3. Read/write text file
The write() Method
It writes the contents to the file in the form of string. It
does not return value. Due to buffering, the string may not
actually show up in the file until the flush() or close()
method is called.
The read() Method
It reads the entire file and returns it contents in the form of
a string. Reads at most size bytes or less if end of file
occurs.if size not mentioned then read the entire file
contents.

File Handling
Read/Write a Text file
write() ,read() Method based program
f = open("a.txt", 'w')
line1 = 'Welcome to python.mykvs.in'
f.write(line1)
line2="nRegularly visit python.mykvs.in"
f.write(line2)
f.close()
f = open("a.txt", 'r')
text = f.read()
print(text)
f.close()
OUTPUT
Welcome to python.mykvs.in
Regularly visit python.mykvs.in
Note : for text file operation file extension should be .txt and opening mode
without ‘b’ & text file handling relevant methods should be used for file
operations.

File Handling
Writelines()
Using writelines() multiple lines can be written in file.
f = open(“d.txt", "a")
f.writelines(["See you soon!", "Over and out."])
f.close()
#open and read the file after the appending:
f = open(“d.txt", "r")
print(f.read())

File Handling
Read Text file
readline([size]) method: Read no of characters from file if size is mentioned till
eof.read line till new line character.returns empty string on EOF.
e.g. program
f.write(line1)
f.write(line2)
f.close()
text = f.readline()
print(text)
text = f.readline()
print(text)
f.close()
OUTPUT

File Handling
Read Text file
readlines([size]) method: Read no of lines from file if size is mentioned or all
contents if size is not mentioned.
e.g.program
f.write(line1)
f.write(line2)
f.close()
text = f.readlines(1)
print(text)
f.close()
OUTPUT
['Welcome to python.mykvs.inn']
NOTE – READ ONLY ONE LINE IN ABOVE PROGRAM.

File Handling
Read a Text File
Iterating over lines in a file
e.g.program
f.write(line1)
f.write(line2)
f.close()
for text in f.readlines():
print(text)
f.close()

File Handling
Read a Text file
Processing Every Word in a File
f.write(line1)
f.write(line2)
f.close()
for word in text.split( ):
print(word)
f.close()
OUTPUT
Welcome
to
python.mykvs.in
Regularly
visit
python.mykvs.in

File Handling
Getting & Resetting the Files Position
The tell() method of python tells us the current position within the file,where as The seek(offset[,
from]) method changes the current file position. If from is 0, the beginning of the file to seek. If it is set
to 1, the current position is used . If it is set to 2 then the end of the file would be taken as seek
position. The offset argument indicates the number of bytes to be moved.
e.g.program
line = 'Welcome to python.mykvs.innRegularly visit python.mykvs.in'
f.write(line)
f.close()
f = open("a.txt", 'rb+')
print(f.tell())
print(f.read(7)) # read seven characters
print(f.tell())
print(f.read())
print(f.tell())
f.seek(9,0) # moves to 9 position from begining
print(f.read(5))
f.seek(4, 1) # moves to 4 position from current location
print(f.read(5))
f.seek(-5, 2) # Go to the 5th byte before the end
print(f.read(5))
f.close()
OUTPUT
0
b'Welcome'
7
b' to
python.mykvs.inrnRe
gularly visit
python.mykvs.in'
59
b'o pyt'
b'mykvs'
b'vs.in'

File Handling
4. Modify a Text file
There is no way to insert into the middle of a file without re-writing
it. We can append to a file or overwrite part of it using seek but if we
want to add text at the beginning or the middle, we'll have to rewrite
it.
It is an operating system task, not a Python task. It is the same in all
languages.
What we usually do for modification is read from the file, make the
modifications and write it out to a new file called temp.txt or
something like that. This is better than reading the whole file into
memory because the file may be too large for that. Once the
temporary file is completed, rename it the same as the original file.
This is a good, safe way to do it because if the file write crashes or
aborts for any reason in between, we still have our untouched
original file.

File Handling
Modify a Text file
Replace string in the same File
fin = open("dummy.txt", "rt")
data = fin.read()
data = data.replace(‘my', ‘your')
fin.close()
fin = open("dummy.txt", "wt")
fin.write(data)
fin.close()
What have we done here?
Open file dummy.txt in read text mode rt.
fin.read() reads whole text in dummy.txt to the variable data.
data.replace() replaces all the occurrences of my with your in the whole text.
fin.close() closes the input file dummy.txt.
In the last three lines, we are opening dummy.txt in write text wt mode and writing the
data to dummy.txt in replace mode. Finally closing the file dummy.txt.
Note :- above program is suitable for file with small size.

File Handling
Modify a Text file
Replace string using temporary file
import os
f=open("d:a.txt","r")
g=open("d:c.txt","w")
text=text.replace('my','your')
g.write(text)
f.close()
g.close()
os.remove("d:a.txt")
os.rename("d:c.txt","d:a.txt")
print("file contents modified")
Note- above program is suitable for large file.Here line by line is being read from a.txt file
in text string and text string been replaced ‘my’ with ‘your’ through replace()
method.Each text is written in c.txt file then close both files ,remove old file a.txt through
remove method of os module and rename c.txt(temporary file) file with a.txt file.After
execution of above program all occurances of ‘my’ will be replaced with ‘your’.For testing
of above program create a.txt file in d: drive with some substring as ‘my’.Run above
program and check changes.

File Handling
5. Append content to a Text file
line = 'Welcome to python.mykvs.innRegularly visit python.mykvs.in'
f.write(line)
f.close()
f = open("a.txt", 'a+')
f.write("nthanks")
f.close()
text = f.read()
print(text)
f.close()
OUTPUT
thanks
A
P
P
E
N
D
C
O
D
E

File Handling
Standard input, output,
and error streams in python
Most programs make output to "standard out“,input from "standard
in“, and error messages go to standard error).standard output is to
monitor and standard input is from keyboard.
e.g.program
import sys
a = sys.stdin.readline()
sys.stdout.write(a)
a = sys.stdin.read(5)#entered 10 characters.a contains 5 characters.
#The remaining characters are waiting to be read.
sys.stdout.write(a)
b = sys.stdin.read(5)
sys.stdout.write(b)
sys.stderr.write("ncustom error message")

File Handling
Write and read a Binary file
#e.g. program
binary_file=open("D:binary_file.dat",mode="wb+")
text="Hello 123"
encoded=text.encode("utf-8")
binary_file.write(encoded)
binary_file.seek(0)
binary_data=binary_file.read()
print("binary:",binary_data)
text=binary_data.decode("utf-8")
print("Decoded data:",text)
Note :- Opening and closing of binary file is same as text file opening and closing.While
opening any binary file we have to specify ‘b’ in file opening mode.
In above program binary_file.dat is opened in wb+ mode so that after writing ,reading
operation can be done on binary file.String variable text hold text to be encoded before
writing with the help of encode method().utf-8 is encoding scheme.after writing text ,we
again set reading pointer at beginning with the help of seek() method.then read the text
from file and decode it with the help of decode() method then display the text.

File Handling
Binary file Operation
using pickle module
The problem with the approach of previous slide comes from the
fact that it is not very easy to use when we want to write several
objects into the binary file. For instance, consider what we would
have to do if we wished to write string, integer and perhaps even
the contents of a list or dictionary into the file. How would we read
the contents of this file later? This is not a trivial task, especially if
some of the objects can have variable lengths.
Fortunately, Python has a module which does this work for us and
is extremely easy to use. This module is called pickle; it provides us
with the ability to serialize and deserialize objects, i.e., to convert
objects into bitstreams which can be stored into files and later be
used to reconstruct the original objects.

File Handling
Binary file Operation
using pickle module
pickle.dump() function is used to store the object data to the file. It
takes 3 arguments.First argument is the object that we want to
store. The second argument is the file object we get by opening the
desired file in write-binary (wb) mode. And the third argument is
the key-value argument. This argument defines the protocol. There
are two type of protocol – pickle.HIGHEST_PROTOCOL and
pickle.DEFAULT_PROTOCOL.
Pickle.load() function is used to retrieve pickled data.The steps are
quite simple. We have to use pickle.load() function to do that. The
primary argument of pickle load function is the file object that you
get by opening the file in read-binary (rb) mode.

File Handling
Binary file R/W Operation
using pickle module
import pickle
output_file = open("d:a.bin", "wb")
myint = 42
mystring = "Python.mykvs.in!"
mylist = ["python", "sql", "mysql"]
mydict = { "name": "ABC", "job": "XYZ" }
pickle.dump(myint, output_file)
pickle.dump(mystring, output_file)
pickle.dump(mylist, output_file)
pickle.dump(mydict, output_file)
output_file.close()
input_file = open("d:a.bin", "rb")
myint = pickle.load(input_file)
mystring = pickle.load(input_file)
mylist = pickle.load(input_file)
mydict = pickle.load(input_file)
print("myint = %s" % myint)
print("mystring = %s" % mystring)
print("mylist = %s" % mylist)
print("mydict = %s" % mydict)
input_file.close()
In this program we open a.bin file in
binary mode using ‘wb’ specification
and create and store value in 4
different data objects i.e.
int,string,list,dict.Write these into
binary file using pickle.dump()
method then close this file and open
the same for reading operation.We
read the content using load method()
and display the value read from file.
To use dump and load we have to
import pickle module first of all.

File Handling
Iteration over
Binary file - pickle module
import pickle
output_file = open("d:a.bin", "wb")
myint = 42
mystring = "Python.mykvs.in!"
mylist = ["python", "sql", "mysql"]
mydict = { "name": "ABC", "job": "XYZ" }
pickle.dump(myint, output_file)
pickle.dump(mystring, output_file)
pickle.dump(mylist, output_file)
pickle.dump(mydict, output_file)
output_file.close()
with open("d:a.bin", "rb") as f:
while True:
try:
r=pickle.load(f)
print(r)
print(“Next data")
except EOFError:
break
f.close()
Read objects
one by one

File Handling
Insert/append record in a Binary file
- pickle module
rollno = int(input('Enter roll number:'))
name = input('Enter Name:')
marks = int(input('Enter Marks'))
#Creating the dictionary
rec = {'Rollno':rollno,'Name':name,'Marks':marks}
#Writing the Dictionary
f = open('d:/student.dat','ab')
pickle.dump(rec,f)
f.close()
Here we are creating
dictionary rec to dump
it in student.dat file

File Handling
Read records from a Binary file
- pickle module
f = open('d:/student.dat','rb')
while True:
try:
rec = pickle.load(f)
print('Roll Num:',rec['Rollno'])
print('Name:',rec['Name'])
print('Marks:',rec['Marks'])
except EOFError:
break
f.close()
Here we will iterate
using infinite while
loop and exit on end of
file is reached.at each
iteration a dictionary
data is read into rec
and then values are
being displayed

File Handling
Search record in a Binary file
- pickle module
flag = False
r=int(input(“Enter rollno to be searched”))
while True:
try:
if rec['Rollno'] == r:
print('Roll Num:',rec['Rollno'])
print('Name:',rec['Name'])
print('Marks:',rec['Marks'])
flag = True
except EOFError:
break
if flag == False:
print('No Records found')
f.close()
Here value of r to be
searched will be compared
with rollno value of file in
each iteration/next record
and if matches then
relevant data will be shown
and flag will be set to True
otherwise it will remain
False and ‘No Record Found
message will be displayed’

File Handling
Update record of a Binary file
- pickle module
reclst = []
r=int(input(“enter roll no to be updated”))
m=int(input(“enter correct marks”))
while True:
try:
reclst.append(rec)
except EOFError:
break
f.close()
for i in range (len(reclst)):
if reclst[i]['Rollno']==r:
reclst[i]['Marks'] = m
f = open('d:/student.dat','wb')
for x in reclst:
pickle.dump(x,f)
f.close()
Here we are reading all records from
binary file and storing those in reclst
list then update relevant roll no
/marks data in reclst list and create
/replace student.dat file with all
data of reclst.
If large data are in student.dat file
then It’s alternative way can be
using temporary file creation with
corrected data then using os module
for remove and rename method
(just similar to modification of text
file)

File Handling
Delete record of a Binary file
- pickle module
reclst = []
r=int(input(“enter roll no to be deleted”))
while True:
try:
reclst.append(rec)
except EOFError:
break
f.close()
f = open('d:/student.dat','wb')
for x in reclst:
if x['Rollno']==r:
continue
pickle.dump(x,f)
f.close()
Here we are reading all records from
binary file and storing those in reclst
list then write all records except
matching roll no(with the help of
continue statement) in student.dat
file.Due to wb mode old data will be
removed.
If large data are in student.dat file
then It’s alternative way can be
using temporary file creation with
corrected data then using os module
for remove and rename method
(just similar to deletion from text
file)

File Handling
Download python file/program for
interactive binary data file handling (includes
insert/search/update/delete opeartion)

File Handling
CSV FILE
(Comma separated value)
CSV (Comma Separated Values) is a file format for data storage which looks like a
text file. The information is organized with one record on each line and each field
is separated by comma.
CSV File Characteristics
• One line for each record
• Comma separated fields
• Space-characters adjacent to commas are ignored
• Fields with in-built commas are separated by double quote characters.
When Use CSV?
• When data has a strict tabular structure
• To transfer large database between programs
• To import and export data to office applications, Qedoc modules
• To store, manage and modify shopping cart catalogue

File Handling
CSV FILE
(Comma separated value)
CSV Advantages
• CSV is faster to handle
• CSV is smaller in size
• CSV is easy to generate
• CSV is human readable and easy to edit manually
• CSV is simple to implement and parse
• CSV is processed by almost all existing applications
CSV Disadvantages
• No standard way to represent binary data
• There is no distinction between text and numeric values
• Poor support of special characters and control characters
• CSV allows to move most basic data only. Complex configurations cannot be
imported and exported this way
• Problems with importing CSV into SQL (no distinction between NULL and
quotes)

File Handling
Write / Read CSV FILE
import csv
#csv file writing code
with open('d:a.csv','w') as newFile:
newFileWriter = csv.writer(newFile)
newFileWriter.writerow(['user_id','beneficiary'])
newFileWriter.writerow([1,'xyz'])
newFileWriter.writerow([2,'pqr'])
newFile.close()
#csv file reading code
with open('d:a.csv','r') as newFile:
newFileReader = csv.reader(newFile)
for row in newFileReader:
print (row)
newFile.close()
Writing and reading operation from
text file is very easy.First of all we have
to import csv module for file
operation/method call.
For writing ,we open file in ‘w’ writing
mode using open() method which
create newFile like object.
Through csv.writer() method ,we
create writer object to call writerow()
method to write objects.
Similarly for reading ,we open the file
in ‘r’ mode and create newFile like
object,further we create newfilereader
object using csv.reader()method to
read each row of the file.
Three file opening modes are there
‘w’,’r’,’a’. ‘a’ for append
After file operation close ,opened file
using close() method.

File handling4.pdf

More Related Content

Similar to File handling4.pdf (20)

Recently uploaded (20)

File handling4.pdf