FILE HANDLING IN PYTHON Presentation Computer Science

Chapter - 5
File Handling in PYTHON
File:
 File is the basic unit of storage which used to store the data permanently.
 A file itself is a bunch of bytes stored on some storage device like hard disk or thumb
drive or any secondary storage device
 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.

Data file:
The data files are the files that store data pertaining to a specific application,
for later user. The data file can be stored in two ways:
 TEXT FILE
 BINARY FILE
Text File:
A text file stores information in the form of a stream of ASCII or Unicode
character. In text file, each line of text is terminated, with a special character
known as EOL (End of Line) character. In text files, some internal translation
take place when this EOL character is read or written. In python, by default,
this EOL character is the newline character (‘n’) or carriage-return, new line
character(‘rn’)

Type of text file:
i) Regular Text fie: These are the text files which store the text in the same form as typed. Here the new line character(‘n’)
ends the line and the file extension is .txt.
ii) Delimited text file: In these text files, a specific character is sored to separate the values, i.e., after each value, e.g., a
TAB or a COMMA after every value.
 When a tab is used to separate the values stored, these are called TSV files( Tab Separated Values).These files can
take the extension as .txt or .csv
 When the comma is used to separate the values stored, these are called as CSV files(Comma Separated
Values). These files take extension as .csv
Binary File:
A binary file stores the information in the form of stream of bytes. A binary file contains information in the sam format in
which the information is held in memory, i.e., the file content that is returned a raw format. In binary file, there is no
delimiter character for a line and also no translation occur.
 The CSV format is a popular import and export format for spreadsheet and databases.
 The text files can be opened in any text editor and are in human readable form while binary files are not in
human readable form.
 The .exe files, mp3 file, image files are some of the examples of binary files. we can’t read a binary file using a
text editor.

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 and .rtf are used as
extensions to text files.
Can have any application defined
extension.
There is a delimiting character There is no delimiting character
DIFFERENCE BETWEEN TEXT FILE AND BINARY FILE

Opening and Closing Files:
File handling in Python enables us to create, update, read, and delete the
data 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.
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.

Text file Binary file CSV file
READ()
READLINE()
READLINES()
WRITE()
WRITELINES()
DUMP()
LOAD()
CSV.WRITER()
WRITEROW()
WRITEROWS()
CSV.READER()
COMMON FOR ALL THREE TYPES OF FILES
FILE HANDLING FUNCTIONS:

1.The Open( ) Method:
Before any reading or writing operation of any file, it must be opened first. 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 )
File object: It is an Identifier which acts as an interface between file and the user. It can be called as file
handle.
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.
For example : file1= open(“sample.txt”)
file1= open(“sample.txt”, ”r”)
file mode is optional, default file mode is read only(“r”)

Text file Binary file Description Explanation
‘r’ ‘rb’ Read only File must exist already, otherwise raises I/O error
‘w’ ‘wb’ Write only  If the file does not exist, file is created
 If the file exists, will truncate existing data and
over-write in the file.
‘a’ ‘ab’ Append  File is in write only mode.
 If the file exists, the data in the file is retained and
new data being appended to the end.
 If the file does not exit, python will create a new
file.
FILE ACCESS MODE / FILE OPENING MODE:
The file access mode describes that how the file will be used in the program i.e to read data
from the file or to write data into the file or add the data into the file.

Text file Binary file Description Explanation
‘r+’ ‘ r+b’ or
‘rb+’
Read and
write
 File must exist otherwise error is raised.
 Both reading and writing operations can take place.
‘w+’ ‘w+b’ or
‘wb+’
Write and read  File is created if does not exist.
 If file exists, file is truncated.
‘a+’ ‘a+b’ or
‘ab+’
Write and read  File is created if does not exist.
 If file exists, file’s existing data is retained, new data
is appended.

2. The close() Method:
close(): Used to close an open file. After using this method, an opened file will be closed.
F1 = open(“sample.txt”, “w”)
-----
-----
F1.close()
3. The write() Method
It writes a string the text file.
Syntax:
File-handle. Write( string variable)
Example: s1=“Venkat International public school n“
s2=“Affiliated to CBSE n ”
F1.write(s1)
F1.write(s2)

4. The writelines( ) Method:
It is used to write all the strings in the list as lines to the text file referenced by the file handle.
Systax:
File-Handle.writelines(list)
Example:
f1= open(“sample.txt”, “w”)
l= [ ]
s1=“Venkat International public school “
s2=“nAffiliated to CBSE”
l.append(s1)
l.append(s2)
f1.writelines(l)
Sample.txt
Venkat International Public School
Affiliated to CBSE

5. 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.
Syntax:
File_Handle.read( [ size] )
- size is optional
Example:
f = open(“sample.txt” , ”r”)
1. s= f. read( )
print(s)
o/p: Venkat International Public School
Affiliated to CBSE”
2. s= f.read(6)
print(s)
s=f.read(14)
print(s)
o/p: Venkat
International

6. The readline([size]) method:
It reads a line of input, if n is specified read at most n byte( n characters ) from the text file. It returns the
data in the form string ending with newline (‘n’) character or returns a blank string if no more bytes are left
for reading in the file.
Syntax:
FileHandle.readline( )
Example:
1. f = open(“sample.txt” , ”r”)
s=f.readline()
print(s)
s= f.readline()
print(s)
o/p:
Affiliated to CBSE
2. s=f.readline(20)
print(s)
o/p: Venkat International

7. The readlines( ) method:
It reads all lines from the text file and returns them in a list.
Syntax:
FileHandle.readlines( )
Example:
1. f = open(“sample.txt” , ”r”)
s=f.readlines()
print(s)
o/p:
[“Venkat International Public Schooln”, “Affiliated to CBSEn” ]
2. L =f.readlines()
for i in L:
print(i)
o/p:
Affiliated to CBSE

Operations on Binary file:
Pickle Module:
dump()- It is used to store an object( list or dictionary or tuple…) into a binary
file.
Syntax:
pickle.dump( objectname, file_handle)
Example:
f1=open(“student.dat”, ”wb” )
Rec = [1001,”Raj kumar”, 98.5]
pickle.dump(Rec,f1)

Load( ) - It is used to read an object( list or dictionary or tuple…) from a binary
file.
Syntax:
objectname = pickle.load( file_handle)
Example:
f1=open(“student.dat”, ”rb”)
Rec= pickle.load(f1)
Rec[0]= 1001
Rec[1]=Raj kumar
Rec[2]=98.5

FILE HANDLING IN PYTHON Presentation Computer Science

import pickle
def Create( ):
f1= open("employee.dat","wb")
while True:
empid= int(input("Enter the employee id : "))
ename=input("Enter the employee name ")
salary=int(input("Enter the Salary "))
Rec= [empid, ename, salary ]
pickle.dump(Rec, f1 )
ch=input("Do you want to create another record y/ n ")
if ch=="n" or ch=="N":
break
f1.close()

def Display():
f1=open("employee.dat","rb")
try:
while True:
Rec=pickle.load( f1 )
print("Employee Id :", Rec[0])
print("Employee Name :", Rec[1])
print("Salary :", Rec[2])
print( )
except EOFError:
f1.close()

CSV FILES
The separator character of CSV files is called a delimiter. Default and most
popular delimiter is comma. Other popular delimiters include the tab (t),
colon(:), pipe(|) and semi-colon(;) characters.
The csv module of python provides functionality to read and write tabular data
in csv format. It provides two specific types of objects- the reader object and
writer objects- to read and write into CSV files. The csv module’s reader and
writer objects read and write delimited sequences as records in a CSV files.
Opening a CSV file:
Syntax:
File-handle = open(“filename.csv”, “mode” [, newline=’n’])

csv.writer( )
csv files are delimited flat files and before writing onto them, the data must be in
csv-writable-delimited form, it is important to convert the received user data into the form
appropriate for the csv files.
This task is performed by the writer object.
Systax:
Writer-object-name= csv.writer(file-handle[, delimiter character] )
example:
wr= csv.writer(f1, delimiter=‘,’)

csv.wrirerow( ): it writes one row of information onto the csv-file.
Syntax:
Writer-object.writerow(sequence )
csv.wrirerows( ): it writes multiple rows of information onto the csv-file.
Syntax:
Writer-object.writerows(sequence )

csv.reader():
The csv reader object loads data from the csv file, parses it, ie removes
the delimiters and returns the data in the form of a python iterable
wherefrom we can fetch one row of data at a time.
Syntax:
List= cse.reader(filehandle [, delimiter=‘ delimiter character])

Random Access on file:
tell( ) - functions returns the current position of file pointer
in the file.
Syntax:
File-object.tell()
Initial position of file pointer is zero.

seek() -function changes the position of file pointer to the
specified place in the file.
Systax:
File-object.seek(offset ,[ mode])
Offset- specify the no. of bytes
Mode – 0 from beginning of the file
1 from the current position
2 from the end of the file.

Sample.txt
The csv module of python provides functionality to read
and write tabular data in csv format. It provides two
specific types of objects- the reader object and writer
objects- to read and write into CSV files. The csv
module’s reader and writer objects read and write
delimited sequences as records in a CSV files.
F1= open(“sample.txt”, “r”)

FILE HANDLING IN PYTHON Presentation Computer Science

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