report code error found within Instrument.py, while Measuring with Keithley 6517B Electrometer
This is the basic code

`pAmeter=Keithley6517B('ASRL6::INSTR')
id=pAmeter.id
print(id)
#pAmeter.reset()
df=pAmeter.measure_current(0.1,1.05e-11)
sleep(0.1)
a=pAmeter.current
print(a)`

Type error see below:

> KEITHLEY INSTRUMENTS INC.,MODEL 6517B,4402161,A13/700x
Traceback (most recent call last):
  File "path\\to\\file/pAmeter_6517B_test.py", line 24, in <module>
    a=pAmeter.current
  File "path\\to\\python\\lib\\site-packages\\pymeasure\\instruments\\instrument.py", line 233, in fget
    return get_process(vals)
TypeError: extract_value() missing 1 required positional argument: 'result'

Correction
###  in instrument.py line 233, 
the return of method fget() should be:
`return get_process(self,vals)`  instead of `return get_process(vals)`

I hope this issure will be fixed soon^OO^

diff --git a/pymeasure/instruments/keithley/keithley6517b.py b/pymeasure/instruments/keithley/keithley6517b.py
index 8dd931be..d0b5e37a 100644
--- a/pymeasure/instruments/keithley/keithley6517b.py
+++ b/pymeasure/instruments/keithley/keithley6517b.py
@@ -66,7 +66,8 @@ class Keithley6517B(Instrument, KeithleyBuffer):
         cast=bool
     )
 
-    def extract_value(self, result):
+    @staticmethod
+    def extract_value(result):
         """ extracts the physical value from a result object returned
             by the instrument """
         m = re.fullmatch(r'([+\\-0-9E.]+)[A-Z]{4}', result[0])
['pymeasure/instruments/keithley/keithley6517b.py']