What Do Square Brackets in Python Function/Class Documentation Signify?

Demystifying Square Brackets in Function/Class Documentation

When encountering square brackets within function or class documentation, it's essential to understand their significance. In Python, square brackets are commonly used to indicate optional arguments.

Case Study: csv.DictReader

Let's take the example of csv.DictReader, a Python module for working with comma-separated value (CSV) files. The following is an excerpt from its documentation:

class csv.DictReader(csvfile[, fieldnames=None[, restkey=None[, restval=None[, dialect='excel'[, *args, **kwds]]]]])

The square brackets indicate that all arguments except for csvfile are optional. For instance, you can initialize the DictReader class by passing only the csvfile argument:

<code class="python">import csv
with open('data.csv') as f:
    reader = csv.DictReader(f)</code>

However, if you wish to specify optional arguments, you can do so in two ways:

1. Positional Arguments:

Pass the arguments in the order they appear in the documentation, skipping optional arguments:

<code class="python">with open('data.csv') as f:
    reader = csv.DictReader(f, fieldnames=['Name', 'Age'])</code>

2. Keyword Arguments:

Specify the argument names explicitly, even if you pass them out of order:

<code class="python">with open('data.csv') as f:
    reader = csv.DictReader(fieldnames=['Name', 'Age'], csvfile=f)</code>

Remember, when using optional arguments, you must always pass the required arguments first. Understanding the syntax of square brackets in function/class documentation empowers you to customize function calls with flexibility and precision.

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