Python File Handling Read Write and Append

Python File Handling

Python has in-built functions and methods to operate files. The common operations used include the opening of a file, the executing of the action (reading, writing or append) and closing a file so as to maintain data integrity.

In Python, file processing involves the use of the open() function, which requires at least one parameter, which is the file path, and an optional second parameter, the mode. The modes specify the way the file is going to be treated:

• r: Read mode; only opens the file in read-only mode (default mode).
• w: Write mode; opens a file in write mode, and truncates the file in the case of an existing file.
• '(a) Appending mode; the file is opened in write mode but when writing data it attempts to append the data at the end of the file.
• r+: Read and write mode; the file opens, and can be read and/or written and does not truncate the file.
• (a+): Append: write after and read; appends and enables reading too.

Such modes are flexible based on your usage case.

Python File Reading

One of the most frequent operations in Python programming is the reading of the files. In order to read a file, you open it in read mode ('r') and then read using the read() method, the readline() or readlines():

• read(): All content of a file is read as a one contiguous string.
• readline(): Useful in processing files line by line as it reads it line per line.

An example of text file reading is given here:

open('example.txt', 'r') as file:

content = file.read()

print(content)

The with statement is more recommended since it automatically closes the file once the block of the code is executed thus ensuring that resources are well utilized as well as preventing occurrence of errors caused by files not being closed appropriately.

Reading per line/chunk wise can be more effective in case of large files and where memory optimization is critical:

open('example.txt', 'r') as file:

with line in file:

print(line.strip())

This technique will not load the whole file into the memory at once, especially in the case of large data files or logs.

Python File Writing

Writing of files can be used to store your data or results of your programs. In order to write to a file one has to open it in writing mode ('w'). In case of the file already being present, opening with write mode will destroy the contents of the file.

The following is an example code to output to file:

using file = open('output.txt', 'w'):

file.write("Hello, World!n")

file.write("This is a line that is written.")

The file, when it does not exist, will be created automatically by Python. Write mode should also be taken with caution as it truncates the already existing files, and therefore all the past information in that file will be lost.

The Python Append Method

You would use append on a file where you would be inserting additional information at the end, but you have no desire to clear out all of the information in the file. It can be used to store information in a log or to serially store data.

Open up the file in append mode, that is, make it append data using a:

open('output.txt', 'a') as file:

file.write("\nThis line is added to the file.")

The append mode does not erase old information but has an addition at the end of the information that has been stored. An append-like mode ('a+') is available as well that combines reading and appending the file content in the same file and is effective when close control of file content is required.

Best Practices and tips on how to handle files.

• Students are always requested to close files once opened. Auto-management of files with the use of statements is the most acceptable practice.
• Catch exceptions by wrapping the code in a block with try and except, to prevent fatal crashing, and where necessary, use file operations with exceptions that the file cannot be found even when the code is not supposed to fail.
• Be cautious of file path problems; absolute paths or the Python os module is better to handle path safety.
• Make sure that the file mode you are using is the applicable one in order to prevent loss of information accidentally.
• In the binary file case, the modes must be designated with a 'b', say, mode 'rb', mode 'wb', or mode 'ab'.

Using Other File Formats

The file handling of Python does not apply just to plain text files. It is applicable even to such formats as CSV, JSON, etc.:

CSV files: This can be both written and read using its csv module providing both reader objects and writer objects that make it convenient to use comma-separated values.

JSON files: The json module makes it possible to read and write json data, which is commonly used to store configuration data and to exchange data.

The example of reading JSON file:

import json

using file = open('data.json', 'r'):

data = json.loads(file)

print(data)

Esporta i dati in JSON:

and with file = open('data.json', 'w'):

json.dump(data, file)

These modules make it easy to deal with the standard data formats in Python programs.

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Conclusion

The ability to read, write and append files is essential in Python to make a successful coder and in managing files. As you know, the processing of any text files can seem simple to handle; nevertheless, complex data such as CSV and JSON files are rather complicated to tackle, but with the help of Python, it is not that difficult to automate. When you practice those skills (as at Uncodemy Python courses), you can build your proficiency as well as prepare yourself to have a career realizing data science and programming.

To bet on Python file handling and use it in projects will definitely help you become a developer. You might want to take a look at what Uncodemy offers to give you a practical experience and the pro tip to fast-track the process of learning Python programming.