File Handling in python

Why ?

Saving the data permanently for the future purpose.

Temporary storage areas : while a program executes, the data stored is required, but once the execution is complete, the data is no longer available.

example of storage structure objects in python : List, tuple, and dictionary
The data will be stored in Python Virtual Machine

Permanent storage area : files and databases are means of storing data permanently stored. On a broad prospective , if you have huge amount of data, go for database,else go for file concept.

File handling concepts

Types:

Text files : text data like names, mark, numbers etc.
Binary files : data like images, video, audio files etc.

Process

Open the file, : for writing or reading

open(filename, mode/purpose)

if the source code and file are in the same folder, only file name with extension is required i.e. in the current working directory, else absolute path is required.

eg: f = open('example.txt','w')

The allowed modes

‘r’ : read operation

Opens an existing file for read operation.

file pointer is pointing to the first position.

If the file is not available, then we will ‘file not found’ error. [PVM checks for the file]

Default mode is read operation
‘w’ : write operation

Opens a file for write operation, if the file is not available, then P.V.M. will create a file.

If this file already contains any data, the data is going to be override.
‘a’ : append operation

Opens a file for append, if file is not available , creates a file.

If the file exists, the data is not going to be override, instead, the file pointer points to the last position and new data will be added as continuation.
‘x’ : exclusive {exclusive write operation}

Exactly same as write operation, but in ‘x’ the file should compulsory not available. The mode creates a new file and starting writing to it.

If file exists already, then ‘File exist error’ is occurred.
‘r+’: read and write

No overriding of existing data
‘w+’: write and read

Override existing data
‘a+’: append and read

It wont override existing data

These modes are applicable only for text files.

For Binary files, there also exists 7 modes :

‘rb’ : read operation

Opens an existing file for read operation.

file pointer is pointing to the first position.

If the file is not available, then we will ‘file not found’ error. [PVM checks for the file]

Default mode is read operation
‘wb’ : write operation

Opens a file for write operation, if the file is not available, then P.V.M. will create a file.

If this file already contains any data, the data is going to be override.
‘ab’ : append operation

opens a file for append, if file is not available , creates a file.

If the file exists, the data is not going to be override, instead, the file pointer points to the last position and new data will be added as continuation.
‘r+b’: read and write

No overriding of existing data
‘w+b’: write and read

Override existing data
‘a+b’: append and read

It wont override existing data
‘xb’ : exclusive

Exactly same as write operation, but in ‘x’ the file should compulsory not available. The mode creates a new file and starting writing to it.

If file exists already, then ‘File exist error’ is occurred.
after performing the required operations, the file should be closed in order to de-allocate the resources allocated for the file object.
- syntax: file_object.close()

Various properties of file object.

// assume f as a file object

f.name name of the file is returned
f.mode opened mode
f.closed is the file is closed
f.readable() a method to check the file is readable or not, returns bool answer
f.writable() a method to check the file is writable or not, returns bool answer

Operation

write operation
- file_object.write(str)
- add ‘\n’ to get into new line
writeline operation
- file_object.writelines(list_of_lines)
- list of lines can be of form list, tuple, or set
- By default, the data will be written to a single line, if you want to be in multiple lines, add a ‘\n’ to the elements.

read operation

file_object.read() # to read total data from the file
file_object.read(n) # to read n characters from file
file_object.readline() # to read single line
file_object.readlines() # to read all lines into a list

Dynamic inputting and outputting

if a single ” is used , it is considered as a escape character, to overcome this problem , use ’\’

example program :

// reading data

// reading first ten characters

// reading a single line.
// new line,i.e. ‘\n’ (escape character) is considered as a single character

while using multiple lines , printing it individually, the output will have extra empty lines as a result of individual print statements

example :

o/p:

here the new line b.w ‘Chinny’ and ‘Bunny’ is due to individual print statements. To resolve the issue, add a parameter , end=”

// reading lines of files as list of lines, hence a loop is used to out the lines

coping data from one file to another file

#consider file input.txt, having input data
#taking input data and coping it to file output.txt
 
f1 = open('input.txt')
f2 = open('output.txt','w')
f2.write(f1.read())
f1.close()
f2.close()

’with open() as ’ operation

// using ‘with open’ approach we do not have to use close() method to explicitly close the file object, the approach will automatically close the file object.

with open('filename.extension','mode') as file_object:
  # perform the necessary operations

// if you are skeptical, use closed() method to check

Creating , renaming and removing file

def renamefile():
    global _FILE
    src = _FILE
    dest = input("Enter the new name for file with extension _ ")
    os.rename(src , dest) # renmae file
    print("File successfully renamed !!")
    _FILE = dest

#create file
_FILE = input("Enter new file name _ ")
            with open(_FILE,'x') as fs :
                pass

#remove file
if os.path.exists(_FILE):
              os.remove(_FILE)
            else:
              print("The file does not exist")

#file handling
import os
_FILE = ""
 
def readfile():
    print("\n-----------------------------------")
    print("      --- Contents of file ----\n")
    global _FILE
    with open(_FILE) as fs:
        print(fs.read())
 
def appendfile():
    global _FILE
    with open(_FILE, 'a') as fs:
            limit = int(input("Enter the no of students "))
            for i in range(limit):
                name = input("\n Enter the name of the student _ ")
                roll = input(" Enter the roll no of the student _ ")
                adddress = input("Enter the address of the student_ ")
                class_name = input("Enter the class of student_ ")
                fs.write(name + '\n')
                fs.write(roll + '\n')
                fs.write(class_name + '\n')
                fs.write(address + '\n')
    
def renamefile():
    global _FILE
    src = _FILE
    dest = input("Enter the new name for file with extension _ ")
    os.rename(src , dest)
    print("File successfully renamed !!")
    _FILE = dest
 
        
def menu():
    global _FILE
    _FILE = input("Enter file name with extension __ ")
    while(1):
        print("\n==================")
        print("1. Create file")
        print("2. Read file")
        print("3. Append file")
        print("4. Rename file")
        print("5. Remove file")
        print("6. quit program")
        print("==================")
        choice = int(input("Enter the choice _ "))
        if choice == 1:
            _FILE = input("Enter new file name _ ")
            with open(_FILE,'x') as fs :
                pass
        elif choice == 2 :
            readfile()
        elif choice == 3:
            appendfile()
        elif choice == 4:
            renamefile()
        elif choice == 5:
            if os.path.exists(_FILE):
              os.remove(_FILE)
            else:
              print("The file does not exist")
        elif choice == 6:
            break
        else:
            print("Not a valid input")
            os.sleep(3)
        
menu()

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