The stepping frequency is how many pulses are sent to the driver in a second. It is set by a combination of how long your program waits after setting the step output high and how long it waits after setting the step output low (both of which are controlled by the delay value in your program):
Frequency = 1 second / (time high + time low)
The Python program you posted should apply a stepping frequency of around 25kHz, which is pretty fast, so you might try running your motor with a stepping frequency as low as a few hundred Hz to see if it works. What is the target speed for your application?
- Patrick