ModulesAndTiming < AFNOG

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---+ Python modules and timing

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
If, in our program which prints "Hello World!" we want to have the text printed only every second we could program this as follows:
<verbatim>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</verbatim>

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

<verbatim>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</verbatim>

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:

<verbatim>from math import sin,radians
print(sin(radians(30)))</verbatim>
---++ Writing your own functions

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 <i>def. </i>The function body is again indented, like we saw in case of the conditions or the loops:
<verbatim>from math import sin,radians
def sin_deg(degrees):
   rad = radians(degrees)
   return sin(rad)</verbatim>

We can call this function as follows:
<verbatim>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)</verbatim>
---++ Plotting a function

<img alt="damped_osc.png" height="46" src="%ATTACHURL%/damped_osc.png" title="damped_osc.png" width="166" /><br />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.
<verbatim>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</verbatim>

When running the program, we can redirect the printed data to a file. On the PC, using CPython (python3) this is done as follows:
<verbatim>python3 damped_osc.py > damped_osc.dat.</verbatim>

We can however also run the code on the ESP32 and redirect the output to a file on the PC:
<verbatim>ampy run damped_osc.py > damped_osc.dat</verbatim>

Once we have the data in a file, we call gnuplot:
<verbatim>gnuplot
plot "damped_osc.dat" with lines

</verbatim>

<img alt="damped_osc_plot.png" height="598" src="%ATTACHURL%/damped_osc_plot.png" title="damped_osc_plot.png" width="662" />

<verbatim> </verbatim>

Let's try these [[ExerciseSheets#SecondSession]]<br />Thereafter, we will learn how to access hardware in [[Hardware Access GPIO]]<br /><br />

-- %USERSIG{UliRaich - 2022-10-15}%

---++ Comments

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I	Attachment	History	Action	Size	Date	Who	Comment
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
Topic revision: r5 - 2024-03-28 - UliRaich