Python でファイルの最初の N 行を抽出する方法は?

Retrieving the First N Lines of a File

Often, when working with large raw data files, it becomes necessary to extract a specific number of lines for further processing or analysis. In Python, there are multiple approaches to accomplish this task.

Reading First N Lines Using List Comprehension

A simple and effective method involves utilizing list comprehension:

<code class="python">with open(path_to_file) as input_file:
    head = [next(input_file) for _ in range(lines_number)]
print(head)</code>

This approach iterates through the input file using the next() function and stores the first lines_number lines in the head list.

Using the islice() Function

Another approach leverages Python's itertools module:

<code class="python">from itertools import islice

with open(path_to_file) as input_file:
    head = list(islice(input_file, lines_number))
print(head)</code>

Here, the islice() function is used to iterate over the first lines_number lines of the input file, creating a list of the extracted lines.

Effect of Operating System

The implementation described above should work regardless of the operating system being used. However, it's worth noting that in Python 2, the next() function is known as xrange(), which may require corresponding adjustments in older code bases.

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