python programming

1. Topic: Files Operations
GE 8151 Problem Solving and Python
Programming
Presented by, Dr.G.Rajiv Suresh Kumar,
HoD/CSE,JCTCET

2. FILES
Files
A File is collection of data stored on a secondary storage
device like hard disk. Data on non-volatile storage
media is stored in named locations on the media called
files. File is a named location on disk to store related
information.
While a program is running, its data is in memory. When
the program ends, or the computer shuts down, data in
memory disappears. To store data permanently, you
have to put it in a file. Files are usually stored on a hard
drive, floppy drive, or CD-ROM.

3. File continuation
• When there are a large number of files, they are
often organized into directories (also called
"folders"). Each file is identified by a unique
name, or a combination of a file name and a
directory name.
• Hence, in Python, a file operation takes place in
the following order.
Open a file
Read or write (perform operation)
Close the file

4. File Types
• Text files
• Binary files

5. Text files
• A text file is a file that contains printable
characters and whitespace, organized into
lines separated by newline characters. Text
files are structured as a sequence of lines,
where each line includes a sequence of
characters. Since Python is specifically
designed to process text files, it provides
methods that make the job easy.

6. Binary files
• A binary file is any type of file that is not a text
file. Because of their nature, binary files can
only be processed by an application that know
or understand the file’s structure. In other
words, they must be applications that can read
and interpret binary.

7. File operation
Open a file
Read or write (perform operation)
Close the file

8. Attributes of a file
Attribute Description
file.closed If file is closed return true else false
file.mode Returns one of the modes in which the current file is opened
file.name Returns the name of the file

9. Example for attributes
• fileread= open( “text.txt” , ”r+” )
• print (“Name of the file : ”,fileread.name)
• print (“Closed or not : ”,fileread.closed)
print(“opening mode : ”,fileread.mode)
OUTPUT:
• Name of the file : text.txt
• Closed or not : False
• opening mode : r+

10. Opening a file
• Python has a built-in function open() to open a file.
This function returns a file object, also called a handle,
as it is used to read or modify the file accordingly.
Syntax:
• Fileobject = open(“filename or file path” ,”access
mode”)
• >>> f = open("test.txt") # open file in current directory
by directly specifying the name of the file.
• >>> f = open("C:/Python33/README.txt") # specifying
full path.
• >>> f = open(“test.txt” , “r”) # open the file by
mentioning file name and mode

11. File opening Modes
Mode Description
r Opens a file for reading only. The file pointer is placed at the beginning of the
file. This is the default mode
w Opens a file for writing only.Overwrites the file if the file exists.If the file does
not exist, creates a new file for writing
a Opens a file for appending. The file pointer is placed at the end of the file. If
the file does not exist, creates a new file for writing
r+ Opens a file for both reading and writing. The file pointer is placed at the
beginning of the file.
W+ Opens a file for both reading and writing. Overwrites the file if the file exists.If
the file does not exist, creates a new file for reading and writing.
A+ Opens a file for both reading and appending. The file pointer is placed at the
end of the file. If the file does not exist, creates a new file for reading and
writing.

12. File opening Modes
Mode Description
rb Opens a file for both reading in binary format. The file pointer is placed at the
beginning of the file
wb Opens a file for writing only in binary format.Overwrites the file if the file
exists.If the file does not exist, creates a new file for writing
ab Opens a file for appending in binary format. The file pointer is placed at the end
of the file. If the file does not exist, creates a new file for writing

13. FILE CLOSING
• When the operations that are to be performed o
n a opened file are finished, we have to close the
file in order to release the resources. The closing
is done with a built-in function close()
Syntax:
fileobject.close()
Example:
f= open(“text.txt” , “w”) #open a file
#perform some operations
f.close() #close the file

14. Writing to a file
• After opening a file, we have to perform some operations on the
file. In order to write into a file, we have to open it with w mode, or
a mode, or any other writing – enabling mode. write() method
enables us to write any string to a opened file.
Syntax:
Fileobject=open(“file.txt”,”w”)
Fileobject.write(“String to be written”)
Example:
fo = open("foo.txt", "w")
fo.write( "Python is a great language.nYeah its great!!n");
print(“success”)
fo.close()

15. Reading a file
The text files can be read in four different ways listed below:
Using read Method
Using readlines Method
Using readline Method
Syntax:
read()
<file variable name>.read()
When size is not specified entire file is read and the contents are
placed in the left hand side variable.
<file variable name>.read(<size>)
When size is specified , the size number of characters are read.
When an empty file is read no error is displayed but an empty string
is returned.

16. readlines()
<file variable name>.readlines(<size>) #size optional
When size is not specified entire file is read and
each line is added in a list. When size is specified
, the lines that make up the size bytes are
read.When an empty file is read no error is
displayed but an empty list is returned.

17. Example for all types of reading a file: Assume
the content of a file:
Hello Good morning
We are learning python
Its very interesting

18. Program
fileread = open(“text.txt”, “r”)
Str=fileread.read(10)
Length=len(Str)
print (str)
print (Length)
Str=fileread.read(20)
print (str)
Str= fileread.read()
print (str)
Str=fileread.readlines()
print(Str) fileread.close()

19. Output:
Hello Good
10
morning
We are learn
ing python
Its very interesting
Hello Good morning
We are learning python
Its very interesting

20. Renaming a file
An existing file can be renamed by using the
method rename()
Syntax:
os.rename(current filename, new filename)
Example:
>>> import os
>>>os.rename(“C:/Python27/myfile.txt”,
“C:/Python27/myfile1.txt”)

21. Deleting a File
An existing file can be deleted by using the
method remove().
Syntax:
os.remove(filename)
Example:
>>> import os
>>>os.remove(“C:/Python27/myfile1.txt”)

22. Format Operator
• Definition:
The format operator is used to print the output
in a desired format. The % operator is the
format operator. It is also called as
interpolation operator. The % operator is also
used for modulus. The usage varies according
to the operands of the operator.

23. General syntax:
<format expression>%(values)
# The values is a tuple with exactly the number
of items specified by the format expression.

24. PROGRAM
print(“%d” %(45))
print(“%f”%(3.14159265358979))
print(“%0.2f”%(3.141592653589))
print (“Decimal : %u”%(24))
Print (“Octal : %o”%(24)) Print (“Hexadecimal :
%x”%(1254))
Print (“Hexadecimal : %X”%(1254))
X=40
print(“The given integer is %d”%X)

25. OUTPUT
45
3.141592
3.14
Decimal : 24
Octal : 30
Hexadecimal : 4e6
Hexadecimal : 4E6