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I am trying to get Serial data from my Arduino to my python console

Here is my Arduino code:

void setup() {
  Serial.begin(115200);
  Serial.setTimeout(10);
  randomSeed(analogRead(0));
}

void loop() {
  float x = float(random(0,200))/100;  
  Serial.println(x);
}

I need to get the random variables to my python program. For this i am using Pyserial.

Here is my Python program

import serial
ser = serial.Serial('/dev/ttyACM0',baudrate=115200,timeout=0.1)
ser.flushInput()

while 1:
    sens = ser.read(ser.inWaiting())
    sens = sens[0:len(sens)-2].decode("utf-8")
    print(float(sens))

I am then presented with an Error ValueError: could not convert string to float:

I have tried solving this in multiple ways with no solution. The problem is at the conversion float(sens). I need this data as a float for other operations.

Just to check i ran some changes in the code as such

sens = ser.read(ser.inWaiting())
print(sens,end="\t")
print(type(sens))
sens = sens[0:len(sens)-2]
print(sens,end="\t")
print(type(sens))
sens = sens.decode("utf-8")
print(sens,end="\t")
print(type(sens))

And the output i got was

b'1.89\r\n'     <class 'bytes'>
b'1.89' <class 'bytes'>
1.89    <class 'str'>

As you can see the final variable is a string and it is what i get when i run sens = sens.decode("utf-8") . Yet i still cannot get float data from this string when i run float(sens)

Any workaround or solution to this? I am completely lost.

Edit1: I ran 

>>> float(b'1.80\r\n')
1.8

in another python console and it works completely fine. What's the problem when it is pyserial read ?

SKrish
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2 Answers2

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Try this, if you still having problems, please print value before try cast

Consider to use .strip() to clean input value

b = b'1.89\r\n'
float(b.strip())



float("10") --> 10.0
float("10.2") --> 10.2

float("10,2") --> #CRASH ValueError: invalid literal for float(): 10,22
#SOLUTION
float("10,22".replace(",", ".")) --> 10.22

Conclusion

float(b.strip().replace(",", "."))
Wonka
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  • It's not working. i tried `sens = ser.read(ser.inWaiting()) sens = float(sens.strip().replace(",", ".")) print(sens)`. Now i get the error `TypeError: a bytes-like object is required, not 'str'` – SKrish Feb 25 '20 at 17:57
  • on trying `sens = ser.read(ser.inWaiting()) print(sens) print(repr(sens))` I get `b'1.93\r\n' b'1.93\r\n'`. – SKrish Feb 25 '20 at 18:03
  • I am unsure as to why `float(sens)` does not work even after `sens = sens.decode("utf-8")`. But i checked the variable type and it comes out to `` and still cannot be converted to float? – SKrish Feb 25 '20 at 18:06
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After looking at this for a long time, i found out that initially for a few iterations, the Arduino was sending NULL data. Or rather it was sending b'' serially. And THIS was the issue.

I am now sure since i checked this in a python console.

>>> float(b'1.0')
1.0
>>> float(b'')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: could not convert string to float:

So to overcome this, all i had to do is a simple comparison during every iteration. such as 

if sens != b'':
    continue
else:
    break
SKrish
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