The file concept in python programming

1. File Handling
File
A file or a computer file is a chunk of logically related
data or information which can be used by computer
programs.
File is categorized as either text or binary.
• Text File- Text files are structured as a sequence of
lines, where each line includes a sequence of
characters
• Binary File- A binary file is any type of file that is
not a text file.
Hence, in Python, a file operation takes place in the
following order.
• Open a file
• Read or write (perform operation)
• Close the file

2. The open Function
• Python's built-in open() function is used to open the file.
Syntax: fileobject=open(“filename”,”mode”,”buffering”)
• File name: The file name argument is a string value
• Access mode: The access mode determines the mode in which the file has to be opened. The modes are
• Buffering: If the buffering value is set to 0, no buffering takes place. If the buffering value is 1, line buffering is
performed while accessing a file.

3. Write to file
Example: main.py
Write () Method:- The write() method writes any string to an open file.
fo = open("foo.txt", "w")
fo.write("Welcome!!")
fo.close()
Writelines() Method:- Writes a sequence of strings to the file.
fo = open("foo.txt", "w")
lines=["hi all ","good morning"," bye"]
fo.writelines(lines)
fo.write("n KCE")
fo.close()

4. Read From file
Example: main.py
Read () Method:-It is used to read the data from the file.
fo = open("foo.txt", "r")
print(fo.read())
fo.close()
Readline() Method:-It is used to read a single line from the file.
fo = open("foo.txt", "r")
print(fo.readline())
fo.close()
Readlines() Method:-It is used to read many number of lines from the file.
fo = open("foo.txt", "r")
print(fo.readlines())
fo.close()

5. The file Object Attributes
• Once a file is opened and you have one file object, We can get various information related to that file.
>>>fo = open("foo.txt", "w")
>>>print("Name of the file: ", fo.name)
>>>print("Closed or not : ", fo.closed)
>>>print("Opening mode : ", fo.mode)
Name of the file: foo.txt
Closed or not : False
Opening mode : w
Attribute Description
file.closed Returns true if file is closed, false otherwise.
file.mode Returns access mode with which file was opened.
file.name Returns name of the file.

6. Looping over a file object
• When you want to read – or return – all the lines from a file in a more memory efficient, and fast manner,
you can use the loop over method.
Example:
f = open("foo.txt", "r")
for line in f:
print(line)

7. f=open("kathir","w")
f.writelines("EEEnECEnITnCSnETEnMECH")
f.close()
f=open("kathir","r")
for i in f.readlines():
k=i.split()
for j in k:
print(j)
f.close()
f=open('h1','w')
f.writelines("ExcellentnGoodnBetter
")
f.close()
f=open('h1','r')
for i in f:
print(f.read())
f.close()

8. With Statement
• user can also work with file objects using the with statement.
• One bonus of using this method is that any files opened will be closed automatically after you are done.
Syntax: - with open(“filename”) as file:
Example:
with open("hello.txt", "w") as f:
f.write("Hello World")

9. with open("w1.txt", "w") as f:
f.write("1n2n3n4")
with open("w1.txt", "r") as f:
total=0
for line in f:
num = int(line)
total += num
print("sum",total)

10. File Positions
• tell() :- The tell() method tells the current position within the file.
Syntax: fileobject.tell()
fo = open("foo.txt", "w")
fo.write("Welcome to the world of jumangi n mayajal")
fo.close()
fo=open("foo.txt",'r')
print(fo.tell())
print(fo.read(6))
print(fo.tell())

11. File Positions cont..
• seek() :- This method changes the current file position. f.seek(0,2)- gives the total no of characters in a given file
• The offset argument indicates the number of bytes to be moved.
Syntax:
fileobject.seek(offset)
fo = open("foo.txt", "w")
fo.write("Welcome to the world of jumangi n mayajal")
fo.close()
fo=open("foo.txt",'r')
print(fo.seek(23))
print(fo.read())

12. f=open('h1','w')
f.write("I love this
worldn")
f.writelines("Course Plus
n the Full Specialization
n Shareable Certificates")
#print(f.truncate(7))
f.close()
f=open('h1','r')
print(f.seek(0,2))
f.close()

13. File methods
• A file object is created using open function and here is a list of functions which can be called on this object

14. character=input("Enter the character to find its
occurrence")
f=open("input.txt","r")
count=0
for line in f:
for i in line:
if i.casefold()==character:
count=count+1
print("{} occurs {}" .format(character,count))
f.close()

15. f=open("input.txt","r")
count=0
for line in f:
for i in line.split():
count=count+1
print("occurs {}" .format(count))
f.close()
word=input("Enter the word you want to
count")
f=open("input.txt","r")
count=0
for line in f:
for i in line.split():
if i.casefold()==word:
count=count+1
print("{}occurs {}" .format(word,count))
f.close()
Number of words in the given text file
f=open("input.txt","r")
counts = list()
count=0
for lines in f:
words=lines.split()
for word in words:
counts.append(word)
if word in counts:
count=count+1
else:
count=1
print(“occurs”,count)
Number of specific word in the given text file

16. class FileIO(Exception):
def fun(self):
print("Error! No such file." )
try:
def exists(filename):
try:
f = open(filename)
f.close()
return True
except IOError:
return False
fn=input("enter your file name")
print(fn)
x=exists(fn)
print(x)
if x == True:
print("carry on with your file operation")
f=open(fn)
print(f.read())
else:
raise FileIO
except FileIO as e:

17. fo=open(“input.txt","r")
counts = dict()
for lines in fo:
words=lines.split()
for word in words:
if word in counts:
counts[word] += 1
else:
counts[word] = 1
print(counts)

18. f=open('h1','w')
f.writelines("Course Plus n the Full
Specialization n Shareable Certificates")
f.close()
try:
f=open('h2','r')
for i in f:
print(f.read())
f.close()
except Exception as e:
print (e)

19. File methods cont…

20. Example :
fileno ( ):-
fo = open(“foo.txt", "w")
print ("Name of the file: ", fo.name)
print ("File Descriptor: ", fo.fileno())
fo.close()
next()
fd=open("hari.txt","r")
for index in range(1,3):
line=next(fd,-1)
print(index,line)

21. Pickle
• It is used for serializing and de-serializing a Python object structure.
• Pickling is a way to convert a python object (list, tuple, set, dictionary) into a
character stream import the module through this command:
• import pickle has two main methods: dump() and load().
Dump()-Used to dumps an object to a file object
Load()-Used to loads an object from a file object.
Syntax:
pickle.dump(value,fileobject)
variable=pickle.load(fileobject)

22. Example
import pickle
f1=open("pickle1.txt","wb")
#list,set,tuple,dictionary
set={10:'ram',20:'raj',30:'sam'}
pickle.dump(set,f1)
f1.close()
f2=open("pickle1.txt","rb")
list2=pickle.load(f2)
print("in tuple",list2)
f2.close()

23. Class object Serialization
class Employee:
def __init__(self,Empid=None,Empname=None,Empsalary=None):
self.__Empid=Empid
self.__Empname=Empname
self.__Empsalary=Empsalary
def get_empid(self):
return self.__Empid
def get_empname(self):
return self.__Empname
def get_empsalary(self):
return self.__Empsalary
def set_empid(self, value):
self.__Empid = value
def set_empname(self, value):
self.__Empname = value
def set_empsalary(self, value):
self.__Empsalary = value
def __repr__(self):
return "Employee id {}nEMployee Name {}nEmployee
Salary{}".format(self.get_empid(),self.get_empname(),self.get_empsalary())
import pickle
f1=open("f1.txt","wb")
li=[[101,'sam',25000],[125,"Bob",145000]]
for i in li:
obj=Employee()
obj.set_empid(i[0])
obj.set_empname(i[1])
obj.set_empsalary(i[2])
pickle.dump(obj,f1)
f1.close()
f2=open("f1.txt","rb")
for i in range(len(li)):
dobj=pickle.load(f2)
print(dobj)
f2.close()
2
1
3
4
5

24. Create a student object having properties name, date of
birth, department, semester.
Let the employee class have appropriate getter/setters
methods for accessing these properties.
Initialize these properties through the setter methods.
Store this object into a file "OutObject.txt".
Read the same object from the same file and display its
properties through getter methods.

25. Shelve
• It is used for serializing and de-serializing a Python object structure.
• In pickle random access of an object is not possible where as it is possible
using shelve.
• The shelve module can be used as a simple persistent storage option
for Python objects when a relational database is overkill. The shelf is
accessed by keys, just as with a dictionary.
• The values are pickled and written to a database created and managed by
anydbm
Example :
import shelve
s=shelve.open("file1.txt","c")
l1=[10,20,30]
l2=[30,40]
s["lis1"]=l1[1]
for i,j in s.items():
print (i,j)
'c' flag tells shelve to open the file for reading and writing