Python Files

Python Files

File is a named location in disk to store data. In Python, a file operation takes place in the following order.

• Open a file
• Read or write (perform operation)
• Close the file

Python can process two types of files

• Text file (default)
• Binary file

Text file:

A text file is nothing but which is containing alphabates,numbers,symbols,no specific formatings it is called Text file.
Text file contains alphabets , numbers , symbols.

Binary file:

File not readable by human and understandable by machines.

To Open File:

File is opened using open() and it will return file descriptor.

Listed down modes available to open a file

F = open(“test_sample.txt”) #to open file in current directory
F= open(“D:/Documents:/README.txt”) #specifying full path
By default file will be opened in read mode in text format
The default is reading in text mode. In this mode, we get strings when reading from the file.
In open() method explicitly need to mention mode = ‘b’ if you want to open binary files
Example:
images or exe files)

F = open(“sample_new.txt”) #this as well as mode = ‘r’ both are similar
F= open(“sample_new”,’w’) #performs write operation in text file
F= open(“animal.bmp”,’r+b’) #performs read and write in binary file

To close file:

f.close() ->to perform file close operation
Python will automatically delete all cleanup resources like deleting objects or closing files at the end of our program execution , to avoid data corruption ->programmer need to explicitly close the file.
f.close() ->need to be performed by programmer to ensure that data written to file buffer is flushed to disk (this happens only if the file is closed properly)
f.open(“msg.txt”,’w’)
f.write(“world”)
f.close()
In the above mentioned scenario , there may be chances of exception is raised during file write operations and file is not closed properly.
Better way to achieve this
f = open(“msg.txt”,”w”)
try :
f.write(“Good morning”)
Finally:
f.close()

Writing into a file using write()

Writing into a file is achieved using ‘x’ ,’a’,’w’,’r+’ modes
Return value :Number of bytes written

Code snippet:

with open(“sample_new.txt”,mode=’w’,encoding = ‘utf-8’) as fp:
fp.write(“This is first line\n”)
fp.write(“This is second line”)
fp.write(“This is third line”)
’sample_new.txt’ will get created if it does not exist. If it does exist, it is overwritten , the old content will be truncated

Reading a file using read()

Code snippet:

F=open(“sample_new.txt”,encoding=’utf-8’)
F.read(4)     #reads first 4 bytes —>’This’
F.read(4)     #reads next 4 bytes –>’ is ’
F.read()      #reads the entire content of file from current file pointer
First line
This is second line
This is third line
F.read()      #further reading returns empty string

Moving File point cursor to required location

tell ->returns current file pointer location
Seek(from_what,offset) ->moves file pointer to the location specified

f.seek(from_what,offset)
Possible values of from_what
0 ->moves file pointer to begging to file
1 ->moves file pointer to current location
2 ->moves file pointer to end of file
It will move the file pointer to the location based of from_what value and from there file pointer will be moved to number of bytes mentioned as offset.

Example :

f.seek(0,10)
->from starting of file , file pointer f will be moved 10 bytes
f.seek(1,10)
->from current file pointer will be moved 10 bytes
f.tell() ->to get the exact bytes where the file pointer is currently available
To read file contents line by line
Reading a file line by line using for loop

Code Snippet :

with open (“file_context.txt”) as f:
for line in f:
Print(line,end=””)

Output:

This is my first line
This file
Contains three lines

readline()

readline() will read a single line from current file pointer.

Code snippet:

To open a file and read its first and second line using readline()
with open (“file_readline.txt”) as f:
print(f”File first line {f.readline()}”)
print(f”File second line {f.readline()}”)

Output:

File first line This is first line
File second line This is second line

readlines()

readlines() -> to read all lines from file and return it as list.

Code snippet :

With open(“file_sample.txt”)  as f:
Print(f”f.readlines {f.readlines()}”)

Output:

[“This is first line”,”This is second line”,”This is third line”]

Writeline()

To write a single line to the file.

writelines()

writelines() -> to read all lines from file and return it as list.