[Tut] How to Return a File From a Function in Python?

How to Return a File From a Function in Python?

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<p>Do you need to <strong>create a function that returns a file </strong>but you don’t know how? No worries, in sixty seconds, you’ll know! Go! <img src="https://s.w.org/images/core/emoji/14.0.0/72x72/1f447.png" alt="?" class="wp-smiley" style="height: 1em; max-height: 1em;" /></p>
<p class="has-pale-cyan-blue-background-color has-background">A Python function can return any object such as a file object. To return a file, first open the file object within the function body, handle all possible errors if the file doesn’t exist, and return it to the caller of the function using the <a title="Return Keyword in Python – A Simple Illustrated Guide" rel="noreferrer noopener" href="https://blog.finxter.com/python-return/" target="_blank">keyword </a>operation <code>return open(filename, mode='r')</code>. </p>
<p>Here’s a minimal example that tries to open a filename that was provided by the user via the <code><a rel="noreferrer noopener" href="https://blog.finxter.com/python-input-function/" data-type="post" data-id="24632" target="_blank">input()</a></code> function. If it fails, it <a href="https://blog.finxter.com/python-print/" data-type="post" data-id="20731" target="_blank" rel="noreferrer noopener">prints</a> an error message and asks for a different user input:</p>
<pre class="EnlighterJSRAW" data-enlighter-language="python" data-enlighter-theme="" data-enlighter-highlight="5" data-enlighter-linenumbers="" data-enlighter-lineoffset="" data-enlighter-title="" data-enlighter-group="">def open_file(): while True: filename = input('filename: ') try: return open(filename, mode='r') except: print('Error. Try again') f = open_file()
print(f.read()) </pre>
<p>If I type in the correct file right away, I get the following output when storing the previous code snippet in a file named <code>code.py</code>—the code reads itself (meta <img src="https://s.w.org/images/core/emoji/14.0.0/72x72/1f92f.png" alt="?" class="wp-smiley" style="height: 1em; max-height: 1em;" />):</p>
<pre class="EnlighterJSRAW" data-enlighter-language="python" data-enlighter-theme="" data-enlighter-highlight="" data-enlighter-linenumbers="" data-enlighter-lineoffset="" data-enlighter-title="" data-enlighter-group="">filename: code.py
def open_file(): while True: filename = input('filename: ') try: return open(filename, mode='r') except: print('Error. Try again') f = open_file()
print(f.read())</pre>
<p>Note that you can open the file in <strong><em>writing mode</em></strong> rather than reading mode by replacing the line with the <code>return</code> statement with the following line:</p>
<pre class="EnlighterJSRAW" data-enlighter-language="python" data-enlighter-theme="" data-enlighter-highlight="" data-enlighter-linenumbers="" data-enlighter-lineoffset="" data-enlighter-title="" data-enlighter-group="">open(filename, mode='w')</pre>
<p>A more Pythonic way, in my opinion, is to follow the <a rel="noreferrer noopener" href="https://blog.finxter.com/tips-to-write-clean-code/" data-type="post" data-id="17059" target="_blank">single-responsibility pattern</a> whereby a function should do only one thing. In that case, provide the relevant input values into the function like so:</p>
<pre class="EnlighterJSRAW" data-enlighter-language="python" data-enlighter-theme="" data-enlighter-highlight="" data-enlighter-linenumbers="" data-enlighter-lineoffset="" data-enlighter-title="" data-enlighter-group="">def open_file(filename, mode): try: return open(filename, mode=mode) except: return None def ask_user(): f = open_file(input('filename: '), input('mode: ')) while not f: f = open_file(input('filename: '), input('mode: ')) return f f = ask_user() print(f.read()) </pre>
<p>Notice how the file handling of a single instance and the user input processing are separated into two functions. Each function does one thing only. <a href="https://blog.finxter.com/the-unix-philosophy/" data-type="post" data-id="19704" target="_blank" rel="noreferrer noopener">Unix style.</a></p>
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<h2>Related Tutorials</h2>
<ul>
<li><a rel="noreferrer noopener" href="https://blog.finxter.com/python-return-string-from-function/" data-type="post" data-id="784920" target="_blank">Python Return String From Function</a></li>
<li><a href="https://blog.finxter.com/python-return-dictionary-from-function/" data-type="post" data-id="34362" target="_blank" rel="noreferrer noopener">Python Return Dict From Function</a></li>
<li><a href="https://blog.finxter.com/python-return-set-from-function/" data-type="post" data-id="34346" target="_blank" rel="noreferrer noopener">Python Return Set From Function</a></li>
</ul>
<h2>Programmer Humor</h2>
<pre class="wp-block-preformatted has-global-color-8-background-color has-background"><code><strong>Q</strong>: How do you tell an introverted computer scientist from an extroverted computer scientist? <strong>A</strong>: An extroverted computer scientist looks at <strong><em>your</em></strong> shoes when he talks to you.</code></pre>
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https://www.sickgaming.net/blog/2022/10/...in-python/