Python libraries are arranged as modules, containing a number of functions and/or classes. These modules must be *imported* before being used. You can either import the complete module, or you can import individual functions or classes to be used.

As an example, let's study the *time* module. In MicrroPython the module is called utime (for micro-time) and it contains functions allowing us to delay execution for a certain amount of time.

- sleep(t) sets the program to sleep for t seconds
- sleep_ms(t) sets the program to sleep for t ms

import utime # import time would work as well for i in range(5): print("Hello World") utime.sleep(1) # delay execution be 1 s, utime.sleep_ms(1000) would do the same. sleep_ms is not available in CPython

The other option is to import just the function to be used:

from utime import sleep_ms for i in range(5): print("Hello World!") sleep_ms(1000) # note that utime in front of the sleep call has been omitted

In i similar way, you may use the functions of the math library:

In order to calculate sin(30 degrees) you need access to the *sin* function. The *sin* function however takes its parameter in radians such that you need the function *radians*, converting values from degrees to radians, in addition.

This is how you would go about:

from math import sin,radians print(sin(radians(30)))

It is easily possible to write your own functions and to create your own modules.

Imagine you want to create a sin function which takes angles in degrees, instead of radians. Let's call the function *sin_deg(degrees).* It will take its parameter degrees, convert the value to radians and return the sin result, which was calculated with the sin function from the math library. You can define a function with the keyword *def. *The function body is again indented, like we saw in case of the conditions or the loops:

from math import sin,radians def sin_deg(degrees): rad = radians(degrees) return sin(rad)

We can call this function as follows:

angle = 30 # use 30 degrees as parameter value result = sin_deg(angle) # calculates the sin of "angle" degrees using our own sin_deg function print("sin(",angle,") = ",result)

is the formula for a damped oscillator. In order to plot its shape, we can first define a function which calculates its value for a given x. After that, we call this function for as many points as we want to plot, and we print the x and damped_osc(x) values.

from math import exp,sin def damped_osc(x): # calculates the damped # oscillator function return exp(-1/10)*sin(x) for i in range(500): # calculate 500 values print(i/10,damped_osc(i/10) # and print them

When running the program, we can redirect the printed data to a file. On the PC, using CPython (python3) this is done as follows:

python3 damped_osc.py > damped_osc.dat.

We can however also run the code on the ESP32 and redirect the output to a file on the PC:

ampy run damped_osc.py > damped_osc.dat

Once we have the data in a file, we call gnuplot:

gnuplot plot "damped_osc.dat" with lines

Let's try these ExerciseSheets#SecondSession

Thereafter, we will learn how to access hardware in Hardware Access GPIO

I | Attachment | History | Action | Size | Date | Who | Comment |
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png | damped_osc.png | r1 | manage | 3.3 K | 2022-10-23 - 19:20 | UliRaich | |

png | damped_osc_plot.png | r1 | manage | 38.5 K | 2022-10-23 - 19:33 | UliRaich |

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