Python File Handling

In this article, we are going to discuss Python File handling.

Definition
In Python, a file is a location on disk used to store information, which some names are associated with it. It is used to store data permanently in a non-volatile (non-volatile means retains data even if power loss) memory (Ex: hard disk).

Syntax
file_pointer = open(filelocation, modes, encoding= encoding_type)
encoding is an optinal parameter

Files can be opened in any of the following modes:

• r –> read mode
• w –> write mode
• a –> append mode
• +  ->  append this to the above modes to open the file for reading and write modes Ex: r+

To open a file in binary mode append “b“ to the above modes.

Ex: To open the file a binary file in readmode use “rb“.

How to enter into python interpreter?

Open Linux terminal and type “python” and hit enter so we will see python interpreter. For python3+ version type “python3”,  we are going to see the following info on the terminal. If we want to check the Python version, type “python -v”.

In Python a file, this  operation is performed in the following order:

1. Open a file
2. Read or write or append: When we specify write mode, the file will be opened in write mode if it exists, otherwise, it is going to create the file. This is applicable for append mode also. In read mode, if file exists, it opens in the read mode, otherwise, throws FileNotFoundError exception.
3. Close the file

Open a file

Inbuilt method open() used.

Ex:

f = open("firstfile.txt")   # In python, default is read mode.
f = open("textfile.txt",'w')  # write in text mode
f = open("abc.bmp",'r+b') # read and write in binary mode

Closing a file

Inbuilt method close() used.

Ex:

fp = open("textfile.txt",encoding = 'utf-8')
# perform some file operations
fp.close()

Safer way to open and close files using exception handling:

try:    
    fp = open("textfile.txt",'r',encoding = 'utf-8')    
    # perform some file operations  
finally:    
    fp.close()

Using this method, we are making sure that the file is closed always.

File operations using with

The best way to perform file operation and most commonly used method with statement. Using this ensures that the file is closed when the block inside with is exited.

Ex:

open(‘textfile.txt’, ‘w’, encoding = 'utf-8') as fp:
#perform some file operations
#statements outside the with block

When we exit with block, the file will be closed automatically.

Write to File

To write into a file, we need to open it in write ‘w’ and append ‘a’.

To write to a file, python has the following inbuilt methods:

write(): This method writes the string to a file.

Ex:

with open("textfile.txt",'w',encoding = 'utf-8') as f:    
    f.write("This is a first line\n")    
    f.write("Good morning\n")    
    f.write("This is a example for file write operation\n")    
    f.write("file contains four lines")

If we open the textfile.txt file, we see the above lines are written successfully.

writelines() : This method writes the list of strings to a file.

Ex:

file_content = ["This is a first line\n","Good morning\n",  
                "This is a example for file write operation\n",  
                "file contains four lines"]    
with open("textfile.txt",'w',encoding = 'utf-8') as f:    
    f.writelines(file_content)

Reading from file

To read a file in Python, we must open the file in reading mode ‘r’.

To read from a file, python has the following inbuilt methods:

read():   

read(4): This method reads the first 4 characters from the file.

Ex:

fp = open("textfile.txt",'r',encoding = 'utf8')#provide location of textfile.txt file
print(fp.read(4))#It will read first 4 characters    
fp.close()

read() : This method reads till end of file.

Ex:

fp = open("textfile.txt",'r',encoding = 'utf8')#provide location of textfile.txt file
print(fp.read())#It will read till EOF  
fp.close()

readline(): This method reads one line at a time.

Ex:

fp = open("textfile.txt",'r',encoding = 'utf8')#provide location of textfile.txt file
print(fp.readline(), end="")#It will read first line    
print(fp.readline(), end="")#It will read second line    
fp.close()

readlines(): This methond read all lines in the file and returns a list.

Ex:

fp = open("textfile.txt",'r',encoding = 'utf8')#provide location of textfile.txt file
print(fp.readlines())# read all ines in the file    
fp.close()

for loop: This is the most commonly used way of reading a file. We can read a file line by line using a forloop. This is an efficient and fast way of reading a file.

Ex:

fp = open("textfile.txt",'r',encoding = 'utf-8')#provide location of textfile.txt file
for line in fp:    
    print(line, end='')    
fp.close()

Traverse in a file

The following methods are used to traverse in a file.

tell(): This method is used to get the current file position in a file.

Ex:

with open("textfile.txt", "r") as fp:#provide location of textfile.txt file  
    fp.read(6)  
    print(fp.tell())  
    fp.close()

seek(): This method used to bring/place file cursor to a given position in a file.

Ex:

with open("textfile.txt", "r") as fp:#provide location of textfile.txt file  
    fp.seek(7)    
    print(fp.readline())

truncate(): This method is used to modify/resize the file to a specified size in a file.

Ex:

#writing to a file  
with open("textfile.txt",'w',encoding = 'utf-8') as f:    
    f.write("This is a first line\n")    
    f.write("Good morning\n")    
    f.write("This is a example for file write operation\n")    
    f.write("file contains four lines")  
#Apply truncate method  
fp = open("textfile.txt", "a")#provide location of textfile.txt file    
fp.truncate(25)    
fp.close()    
#reading the file after the truncate  
fp = open("textfile.txt", "r")    
print(fp.read())

flush() : This method flush/clear a buffer.

Ex:

fp = open("textfile.txt", "w")#provide location of textfile.txt file    
fp.write("good morning!\n")    
fp.flush()    
fp.write("good evening!")  
fp.close()

Conclusion

In Python, a file is a location on a disk that is used to store information. File handling in Python is simple and easy. Also, in Python, different modules are available for handling different typess of files.

Ex:

File type	Python module
csv	csv
xml	xml
excel	xlrd

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