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copied!<p><strong>Answer in one line:</strong></p> <pre><code>''.join(random.choice(string.ascii_uppercase + string.digits) for _ in range(N)) </code></pre> <p>or even shorter starting with Python 3.6 using <a href="https://docs.python.org/3/library/random.html#random.choices" rel="noreferrer"><code>random.choices()</code></a>:</p> <pre><code>''.join(random.choices(string.ascii_uppercase + string.digits, k=N)) </code></pre> <p><strong>A cryptographically more secure version; see <a href="https://stackoverflow.com/a/23728630/2213647">https://stackoverflow.com/a/23728630/2213647</a>:</strong></p> <pre><code>''.join(random.SystemRandom().choice(string.ascii_uppercase + string.digits) for _ in range(N)) </code></pre> <p><strong>In details, with a clean function for further reuse:</strong></p> <pre><code>>>> import string >>> import random >>> def id_generator(size=6, chars=string.ascii_uppercase + string.digits): ... return ''.join(random.choice(chars) for _ in range(size)) ... >>> id_generator() 'G5G74W' >>> id_generator(3, "6793YUIO") 'Y3U' </code></pre> <p><strong>How does it work ?</strong></p> <p>We import <code>string</code>, a module that contains sequences of common ASCII characters, and <code>random</code>, a module that deals with random generation.</p> <p><code>string.ascii_uppercase + string.digits</code> just concatenates the list of characters representing uppercase ASCII chars and digits:</p> <pre><code>>>> string.ascii_uppercase 'ABCDEFGHIJKLMNOPQRSTUVWXYZ' >>> string.digits '0123456789' >>> string.ascii_uppercase + string.digits 'ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789' </code></pre> <p>Then we use a list comprehension to create a list of 'n' elements:</p> <pre><code>>>> range(4) # range create a list of 'n' numbers [0, 1, 2, 3] >>> ['elem' for _ in range(4)] # we use range to create 4 times 'elem' ['elem', 'elem', 'elem', 'elem'] </code></pre> <p>In the example above, we use <code>[</code> to create the list, but we don't in the <code>id_generator</code> function so Python doesn't create the list in memory, but generates the elements on the fly, one by one (more about this <a href="https://stackoverflow.com/questions/231767/the-python-yield-keyword-explained/231855#231855">here</a>).</p> <p>Instead of asking to create 'n' times the string <code>elem</code>, we will ask Python to create 'n' times a random character, picked from a sequence of characters:</p> <pre><code>>>> random.choice("abcde") 'a' >>> random.choice("abcde") 'd' >>> random.choice("abcde") 'b' </code></pre> <p>Therefore <code>random.choice(chars) for _ in range(size)</code> really is creating a sequence of <code>size</code> characters. Characters that are randomly picked from <code>chars</code>:</p> <pre><code>>>> [random.choice('abcde') for _ in range(3)] ['a', 'b', 'b'] >>> [random.choice('abcde') for _ in range(3)] ['e', 'b', 'e'] >>> [random.choice('abcde') for _ in range(3)] ['d', 'a', 'c'] </code></pre> <p>Then we just join them with an empty string so the sequence becomes a string:</p> <pre><code>>>> ''.join(['a', 'b', 'b']) 'abb' >>> [random.choice('abcde') for _ in range(3)] ['d', 'c', 'b'] >>> ''.join(random.choice('abcde') for _ in range(3)) 'dac' </code></pre>

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