Function doesn't return right values

Question

I am stuck on this problem for hours now.

I have written a Python code to read and convert data from a text file and everything is running fine.

simulink_robot_motor1=[]
with open('C:\\Users\...\sensor_data.txt',"r") as data_file:
 rows=0
 for line in data_file:
 rows=rows+1
 columns=len(line.split(","))
 simulink_robot_motor=[[0 for x in range(columns)] for y in range(rows)]
 i=0
 with open('C:\\Users\...\sensor_data.txt',"r") as data_file:
 for line in data_file:
 current_line = line.split(",")
 current_line = list(map(float, current_line))
 simulink_robot_motor[i]=current_line
 i=i+1

I am interested in the simulink_robot_motor variable which has the following results:

[[0.0, 3.6],
[1.6e-06, 3.6],
[4.57e-06, 3.6],
[7.67e-06, 3.6],
[1.09e-05, 3.6],
...

Now, I would like to use this code within a function. So if I call the function the list simulink_robot_motor should be returned.

def get_matlab_sensor_data(): 
 simulink_robot_motor1=[]
 with open('C:\\Users\...\sensor_data.txt',"r") as data_file:
 rows=0
 for line in data_file:
 rows=rows+1
 columns=len(line.split(","))
 simulink_robot_motor=[[0 for x in range(columns)] for y in range(rows)]
 i=0
 with open('C:\\Users\...\sensor_data.txt',"r") as data_file:
 for line in data_file:
 current_line = line.split(",")
 current_line = list(map(float, current_line))
 simulink_robot_motor[i]=current_line
 i=i+1
 return (simulink_robot_motor)

But if I run get_matlab_sensor_data() I get the following result:

 [[0, 3.6],
 [0, 0],
 [0, 0],
 [0, 0],
 [0, 0],
 ...

I tried smaller data sets and also switched off scientific decimal style. However, it still didn't work. Is my loop not running properly?

• David Zemens: might help to provide example input & expected output.

Answer 1

Your return statement is at the incorrect indent level, so it's getting executed too soon inside the for loop and never finishes the loop.

def get_matlab_sensor_data(): 
 simulink_robot_motor1=[]
 with open('C:\\Users\...\sensor_data.txt',"r") as data_file:
 rows=0
 for line in data_file:
 rows=rows+1
 columns=len(line.split(","))
 simulink_robot_motor=[[0 for x in range(columns)] for y in range(rows)]
 i=0
 with open('C:\\Users\...\sensor_data.txt',"r") as data_file:
 for line in data_file:
 current_line = line.split(",")
 current_line = list(map(float, current_line))
 simulink_robot_motor[i]=current_line
 i=i+1
 return (simulink_robot_motor)

Also, you probably don't need to indent the second with statement:

def get_matlab_sensor_data(): 
 simulink_robot_motor1=[]
 with open('C:\\Users\...\sensor_data.txt',"r") as data_file:
 rows=0
 for line in data_file:
 rows=rows+1
 columns=len(line.split(","))
 simulink_robot_motor=[[0 for x in range(columns)] for y in range(rows)]
 i=0
 with open('C:\\Users\...\sensor_data.txt',"r") as data_file:
 for line in data_file:
 current_line = line.split(",")
 current_line = list(map(float, current_line))
 simulink_robot_motor[i]=current_line
 i=i+1
 return (simulink_robot_motor)

Answer 2

First of all, in your original code, you're reading the entire file twice, which isn't necessary. Here's a simplification:

simulink_robot_motor=[]
with open(filename,'r') as data_file:
 for line in data_file:
 current_line = list(map(float, line.split(',')))
 simulink_robot_motor.append(current_line)
print(simulink_robot_motor) # -> [[0.0, 3.6], [1.6e-06, 3.6], [4.57e-06, 3.6], [7.67e-06, 3.6], [1.09e-05, 3.6]]

When you tried to convert your code into a function, there were two problems, one was simulink_robot_motor became a local variable that doesn't exist outside the function. The second was you had a return statement in the second for line in data_file: loop which means it would return after reading only one line.

The following fixes both issues and shows how to use the new function:

def get_matlab_sensor_data():
 results=[]
 with open(filename,'r') as data_file:
 for line in data_file:
 current_line = list(map(float, line.split(',')))
 results.append(current_line)
 return results
simulink_robot_motor = get_matlab_sensor_data()
print(simulink_robot_motor) # -> same results as before

• Denis: Thanks @martineau. You answer helped a lot.
• Denis: I can't due to my low reputation. I will when I will reach a score of 15.