Python Handling Files

Handling Files

File handling is essential for reading data from files, storing output, and working with external data sources in Python.

Opening a File

The open() function is used to open files in Python. It takes two arguments:

File name: The name of the file to open.
Mode: Specifies how the file should be opened (e.g., for reading, writing, or appending).

Example:

f = open('myfile.txt', 'r')  # Opens the file in read mode

File Open Modes

Mode	Description
`'r'`	Open for reading (default). Raises an error if the file does not exist.
`'w'`	Open for writing. Creates a new file or overwrites an existing file.
`'a'`	Open for appending. Creates a new file if it doesn’t exist, and appends to the end of the file.
`'x'`	Open for exclusive creation. Raises an error if the file already exists.
`'t'`	Text mode (default).
`'b'`	Binary mode (used for non-text files like images, videos, etc.).

Reading from a File

Using read(): Reads the entire content of a file as a string.

with open('myfile.txt', 'r') as f:
    content = f.read()
    print(content)

Using readline(): Reads a single line from the file.

with open('myfile.txt', 'r') as f:
    line = f.readline()
    print(line)

Using readlines(): Reads all lines from the file and returns a list of strings.

with open('myfile.txt', 'r') as f:
    lines = f.readlines()
    print(lines)

Writing to a File

Using write(): Writes a string to a file. Overwrites the file if it exists.
```
with open('myfile.txt', 'w') as f:
    f.write('Hello, world!')
```

Using writelines(): Writes multiple lines (provided as a list or iterable) to a file.

lines = ['Line 1\n', 'Line 2\n', 'Line 3\n']
with open('myfile.txt', 'w') as f:
    f.writelines(lines)

Appending to a File

To add content to the end of an existing file, use append mode ('a').

Example:

with open('myfile.txt', 'a') as f:
    f.write('This will be appended.\n')

Closing a File

Always close a file after working with it to release resources. Use close() or the with statement for automatic closure.

Manual closure:

f = open('myfile.txt', 'r')
# Do something
f.close()

Automatic closure using with:

with open('myfile.txt', 'r') as f:
    content = f.read()

File Position: seek() and tell()

seek(offset): Moves the file's position to a specific byte.

Example:

with open('myfile.txt', 'r') as f:
    f.seek(5)  # Move to the 5th byte (skips the first 5 characters)
    data = f.read()
    print(data)

tell(): Returns the current position of the file pointer.

with open('myfile.txt', 'r') as f:
    print(f.tell())  # Prints the current position

Truncating a File: truncate()

Shortens a file to a specified length (in bytes). If no length is provided, it truncates the file from the current position.

It modifies the file permanently.

Example:

with open('myfile.txt', 'w') as f:
    f.write('Hello World!')
    f.truncate(5)  # Keeps only the first 5 bytes
 
with open('myfile.txt', 'r') as f:
    print(f.read())  # Output: Hello

Best Practices

Use with for safe file handling: Automatically closes the file even in case of exceptions.
Use appropriate modes: Choose the correct mode to avoid unintentional data loss.
Validate file paths: Check for file existence and permissions before performing operations.

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