Read Entire File Using open() with read()

Opening a text file and loading its full contents into memory can be done concisely using a context manager. This ensures automatic cleanup of resources.

with open('data.txt', mode='r', encoding='utf-8') as src:
    whole_text = src.read()
    print(whole_text)

The mode='r' flag indicates read-only access. Specifying encoding='utf-8' avoids errors when handling Unicode characters.

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Fetch One Line at a Time Using readline()

To process a file sequentially one line per iteration, repeatedly call readline() until a empty string signals end-of-file.

with open('data.txt', 'r', encoding='utf-8') as src:
    segment = src.readline()
    while segment:
        print(segment, end='')
        segment = src.readline()

Using end='' in print prevents duplication of newline characters already present in the file.

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Load All Lines Into a List via readlines()

Calling readlines() returns a list where each element corresponds to a line from the source file, preserving newline delimiters.

with open('data.txt', 'r', encoding='utf-8') as src:
    line_list = src.readlines()
    for row in line_list:
        print(row, end='')

This approach is suitable when random access to specific lines is needed.

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Iterate Directly Over File Object

File handles in Python are iterable, allowing concise and memory-efficient line-by-line traversal.

with open('data.txt', 'r', encoding='utf-8') as src:
    for row in src:
        print(row, end='')

This method avoids constructing an intermediate list, making it optimal for large files.

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Treat In-Memory String as File with io.StringIO

When dealing with string data structured like file lines, io.StringIO provides a file-like interface for stream operations.

import io

sample = "alpha\nbeta\ngamma"
virtual_file = io.StringIO(sample)

for row in virtual_file:
    print(row, end='')

This is useful for testing or when input originates from sources other than disk storage.