chapter-4-data-file-handlingeng.pdf

Data File Handling
Based on CBSE Curriculum
Class-12
By:
Neha Tyagi, PGT CS
KV No-5, 2nd Shift, Jaipur,
Jaipur Region
Neha Tyagi, KV No-5, Jaipur

Data File Handling
• We have seen yet only the transient programs. The programs which run
for a short period of time and give some output and after that their data is
disappeared. And when we again run those programs then we have to use
new data.
• This is because the data is entered in primary memory which is temporary
memory and its data is volatile.
• Those programs which are persistent i.e. they are always in running or run
for a long time then their data is stored in permanent storage (e.g.
harddisk) . If the program is closed or restarted then the data used will be
retrieved.
• For this purpose the program should have the capability to read or write
the text files or data files. These files can be saved in permanent storage.
• The meaning of File I/O (input-output) is to transfer the data from Primary
memory to secondary memory and vice-versa.
Hard
Disk
Program in RAM
(Random Access
Memory)
User

Why the Files are used?
• The data stored with in a file is known as persistent data because
this data is permanently stored in the system.
• Python provides reading and writing capability of data files.
• We save the data in the files for further use.
• As you save your data in files using word, excel etc. same thing we
can do with python.
• “A File is a collection of characters in which we can perform read
and write functions. And also we can save it in secondary storage.”
Python
Program
External
File
(Secondar
y Storage)
Write to file
(Save)
Read from
file (Load)

Data File Operations
Following main operations can be done on files -
1. Opening a file
2. Performing operations
1. READ
2. WRITE etc.
3. Closing The File
Beside above operations there are some more operations can be done on
files.-
• Creating of Files
• Traversing of Data
• Appending Data into file.
• Inserting Data into File.
• Deleting Data from File.
• Copying of File.
• Updating Data into File.
Open
File
Process
Data
Close
File

File Types
File are of two types –
1. Text File: A text file is sequence of line and line is the
sequence of characters and this file is saved in a permanent
storage device. Although in python default character coding
is ASCII but by using constant ‘U’ this can be converted into
UNICODE. In Text File each line terminates with a special
character which is EOL (End Of Line). These are in human
readable form and these can be created using any text
editor.
2. Binary File: Binary files are used to store binary data such
as images, videos audio etc. Generally numbers are stored
in binary files. In binary file, there is no delimiter to end a line.
Since they are directly in the form of binary hence there is no
need to translate them. That’s why these files are easy and
fast in working.

Opening & Closing Files
• We need a file variable or file handle to work with files in Python.
• This file object can be created by using open( ) function or file( )
function.
• Open( ) function creates a file object, which is used later to access
the file using the functions related to file manipulation.
• Its syntax is following -
<file_object>=open(<file_name>,<access_mode>)
• File accessing modes -
– read(r): To read the file
– write(w): to write to the file
– append(a): to Write at the end of file.
Python
Program
External
File
(Seconda
ry
Storage)
Read from
file (Load)

Opening & Closing Files. . .
Here the point is that the file “Hello.txt” which is used here is pre
built and stored in the same folder where Python is installed.
Opened the File
The file is closed.
Output
A program describing the functions of file handling.

File Modes
Mode Description
r To read the file which is already existing.
rb Read Only in binary format.
r+ To Read and write but the file pointer will be at the beginning of the file.
rb+ To Read and write binary file. But the file pointer will be at the beginning of
the file.
w Only writing mode, if file is existing the old file will be overwritten else the new
file will be created.
wb Binary file only in writing mode, if file is existing the old file will be overwritten
else the new file will be created.
wb+ Binary file only in reading and writing mode, if file is existing the old file will be
overwritten else the new file will be created.
a Append mode. The file pointer will be at the end of the file.
ab Append mode in binary file. The file pointer will be at the end of the file.
a+ Appending and reading if the file is existing then file pointer will be at the end
of the file else new file will be created for reading and writing.
ab+ Appending and reading in binary file if the file is existing then file pointer will
be at the end of the file else new file will be created for reading and writing.

Reading a File
Output
A Program to read
“Hello.txt” File.
Hello.txt file was
created using
notepad.|

Reading a File . . .
Output
Reading first 10
characters from the
file “Hello.txt”
1. We can also use readline( ) function which can read one line at a
time from the file.
2. Same readlines( ) function is used to read many lines.

Writing to a File
Output
A program to write in
“Hello.txt”
This “Hello.txt” is created using above
program.
• We can write characters into file by using following two methods -
1. write (string)
2. writelines (sequence of lines)
• write( ) : it takes a sting as argument and adds to the file. We have to use
‘n’ in string for end of line character .
• writelines ( ) : if we want to write list, tupleinto the file then we use
writelines ( ) function.

Writing to a File. . .
Output
A Program to use writelines()
function
“Hello.txt” File is
created using the
above program.

Writing to a File.
Output
Hello.txt file is opened using “with”.
“Hello.txt” File is
created using the
above program.

Appending in a File
Output
A program to append
into a file “Hello.Txt”
A new data is appended into
Hello.txt by above program.
• Append means adding something new to existing file.
• ‘a’ mode is used to accomplish this task. It means opening a file in
write mode and if file is existing then adding data to the end of the
file.

Writing User Input to the File.
Output
Taking the data from
user and writing this
data to the file
“Student.txt”.
Student File is
created by using
the above
program.

Operations in Binary File.
• If we want to write structure such as list, dictionary etc and also we
want to read it then we have to use a module in python known as
pickle.
• Pickling means converting structure into byte stream before writing
the data into file.
• And when we read a file then a opposite operation is to be done
means unpickling.
• Pickle module has two methods - dump( ) to write and load( ) to read.

Operations in Binary File
• To read Binary file use of load ( ) function -

Relative and Absolute Paths
• We all know that the files are kept in directory which are also
known as folders.
• Every running program has a current directory. Which is
generally a default directory and python always see the default
directory first.
• OS module provides many such functions which can be used to
work with files and directories. OS means Operating System.
• getcwd( ) is a very function which can be used to identify the
current working directory.

Standard File Streams
• We use standard I/O Streams to get better performance from
different I/O devices.
• Some Standard Streams in python are as follows -
– Standard input Stream sys.stdin
– Standard output Stream sys.stdout
– Standard error Stream sys.stderr

Thank you
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