Binomial Tree Generators Panic for order argument values too large

[mtreinish]

Information

• retworkx version: 0.10.2
• Python version: 3.9
• Rust version: 1.55
• Operating system: Linux

What is the current behavior?

When running the binomial tree generator functions retworkx.generators.binomial_tree or retworkx.generators.directed_binomial_tree_graph passing in a large order argument which is far too large for the system will result in a panic either from an overflow or allocation error. For example, on my local system:

import retworkx
graph = retworkx.generators.directed_binomial_tree_graph(64)

yields:

thread '<unnamed>' panicked at 'index out of bounds: the len is 0 but the index is 0', src/generators.rs:1055:28
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
pyo3_runtime.PanicException: index out of bounds: the len is 0 but the index is 0

---

import retworkx
graph = retworkx.generators.directed_binomial_tree_graph(63)

yields

thread '<unnamed>' panicked at 'capacity overflow', library/alloc/src/raw_vec.rs:560:5
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
pyo3_runtime.PanicException: capacity overflow

---

import retworkx
>>> graph = retworkx.generators.directed_binomial_tree_graph(45)

yields

memory allocation of 140737488355328 bytes failed

What is the expected behavior?

These graphs exceed the size of system memory or the max size of a u64/usize and this should be reported to the user instead. We can detect the available memory or the size of order and determine up front if things will overflow or are too large for system memory and return appropriate user facing exceptions.

Steps to reproduce the problem

import retworkx
graph = retworkx.generators.directed_binomial_tree_graph(63)
graph = retworkx.generators.directed_binomial_tree_graph(64)
graph = retworkx.generators.directed_binomial_tree_graph(45)