Generate Python passwords without control characters: slice string.printable[:-6] to avoid newlines, tabs, and spaces

Build a Python password generator that avoids control characters; exclude spaces, tabs, newlines by slicing string.printable[:-6] for one-line output.

When generating passwords from a broad character pool in Python, it’s easy to accidentally include control characters like newline or tab. The result prints across multiple lines, makes logs messy, and is confusing to read. If you’re pulling from string.printable, you are exposed to exactly this pitfall.

Problem overview

A straightforward generator might look like this:

import random
import string
passcode = ''.join(
    random.choices(string.printable, k=random.randint(8, 15))
).replace(' ', '')

This approach removes spaces post hoc, but it still allows characters such as \n, \t, \r, \x0b, and \x0c into the result. Consider how a value containing a newline behaves:

raw_a = '57+%\n:cz'
shown_a = '57+%\\n:cz'

The first string includes an actual newline, the second is how the same sequence might be represented to show it visibly as \n.

What’s actually happening

The issue isn’t about “escape characters” inside the password but about control characters that are part of string.printable. If you inspect that constant, you’ll see digits, letters, punctuation, a space, and then the printable control characters at the end:

'0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ!"#$%&\'()*+,-./:;<=>?@[\\]^_`{|}~ \t\n\r\x0b\x0c'

Those trailing characters are the space followed by tab, newline, carriage return, vertical tab, and form feed. If you allow them, you’ll inevitably get passwords that span lines or include invisible whitespace.

It’s also worth distinguishing representation from value. The backslash is the escape character. A backslash inside a password appears as 'abc\\def' in a representation, but prints and compares as abc\def. This subtlety is visible when printing:

print('\'', len('\''))
print('\\', len('\\'))

The printed output shows a single quote and a single backslash, each with length 1.

Solution

The simplest fix is to select only from the subset of string.printable that excludes the space and the control characters. These are the last six items of the constant, so slicing them off at the source prevents the problem entirely:

import random
import string
safe_passcode = ''.join(
    random.choices(string.printable[:-6], k=random.randint(8, 15))
)

The slice [:-6] removes exactly the trailing six characters: the space and the five control characters. By excluding them up front, your generated password will not contain spaces or control characters. As a side effect, you also avoid accidentally shortening the password below the intended minimum by removing spaces after generation.

If you print the filtered pool, you’ll see only the visible characters:

print(string.printable[:-6])
# 0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ!"#$%&'()*+,-./:;<=>?@[\]^_`{|}~

Why this matters

Passwords with control characters like newline and tab are awkward to display, copy, store, and compare visually. Eliminating them at generation time keeps output one-line, predictable, and easier to handle in logs or UIs. It also prevents silent length changes caused by removing spaces after selection.

Additional considerations

Another practical option is to narrow the character set further to avoid characters that can be problematic in passwords. Using string.ascii_letters + string.digits and, optionally, a few punctuation symbols such as period and underscore helps keep things simple. Alternatively, avoid generating backslashes in the first place if they complicate the workflow.

Conclusion

When building a password generator in Python, be explicit about the allowed character set. If you currently rely on string.printable, slice off the trailing space and control characters with string.printable[:-6] to guarantee single-line, clean output. Understand the difference between a string’s representation and its actual value, especially around backslashes, and consider narrowing the pool to a well-defined subset when necessary.