rstr: Generate Random Strings

3.2.2 · active · verified Fri Apr 10

rstr is a Python helper module designed for easily generating random strings of various types. It is suitable for applications such as fuzz testing, generating dummy data, or creating random values based on regular expressions. The library is currently at version 3.2.2 and is actively maintained.

Warnings

gotcha By default, `rstr` uses Python's `random` module (Mersenne Twister), which is a pseudorandom number generator and is NOT cryptographically secure. Do not use default `rstr` for generating sensitive data like passwords or security tokens.
Fix: For sensitive applications, initialize `Rstr` with `random.SystemRandom()`: `from rstr import Rstr; from random import SystemRandom; secure_rstr = Rstr(SystemRandom())`.
gotcha The `xeger()` function, which generates strings from regular expressions, can be very slow for complex or ambiguous regex patterns, as it may take a long time to find matching strings.
Fix: Simplify regex patterns where possible, or consider using `star_plus_limit` argument of `Xeger` class to control repetition bounds more strictly for performance-critical scenarios. Profile performance with your specific patterns..
gotcha When using `xeger()`, the `*` (zero or more) and `+` (one or more) metacharacters are not truly infinite. They have an arbitrary upper bound of 100 repetitions by default, which might not match expectations for very long strings. The maximum possible is 65535.
Fix: You can explicitly set the `star_plus_limit` when creating an `Xeger` instance to change this upper bound: `xeger_instance = Xeger(star_plus_limit=200); xeger_instance.xeger(r'a*')`..
breaking Version 3.0.0 of `rstr` dropped support for Python 2.x. Attempts to use versions 3.x on Python 2.x environments will result in import errors or other incompatibilities.
Fix: Ensure your project runs on Python 3.7 or newer. If Python 2.x compatibility is required, you must use an older `rstr` version (e.g., <3.0.0), which is not recommended due to lack of maintenance..

Install

pip install rstr Install stable version

Imports

rstr
```
import rstr
```
Rstr
```
from rstr import Rstr
```
xeger
```
from rstr import xeger
```

Quickstart

Demonstrates basic random string generation, fixed-length generation, regex-based generation with `xeger`, and how to use a cryptographically secure random number generator.

import rstr
from rstr import Rstr, xeger
from random import SystemRandom

# Generate a random string from a custom alphabet
print(f"Random string from 'ABC': {rstr.rstr('ABC')}")

# Generate a fixed-length random string
print(f"4-char string from '0123456789': {rstr.rstr('0123456789', 4)}")

# Generate a random string matching a regex pattern
print(f"Random string matching '[a-z]{{5,10}}': {xeger(r'[a-z]{5,10}')}")

# Use a cryptographically secure random source for sensitive cases
cs_rstr = Rstr(SystemRandom())
print(f"Secure random string (16 hex chars): {cs_rstr.rstr('0123456789abcdef', 16)}")

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