Python, use variable as object "name"

Question

I've been getting into Python for a while now, since I'm still a beginner, I try to keep things simple as much as possible. There is however one thing that I would like to be able to do, but cannot get right.

I've searched and found several questions that somewhat resemble, mine, but answers are mostly to use eval() and exec(), which I read is very bad practice. Using a dictionary seems to be another often proposed option, but I don't see how to apply this to my case.

class pthead:
 def __init__(self, name, port):
 self.name = name
 self.port = port
 def initialize(self):
 ser4.write(initialization_commands) # works
 (self.port).write(initialization_commands) # doesn't work
UART.setup("UART4")
ser4 = serial.Serial(port="/dev/ttyO4", baudrate=9600, timeout=0.5)
head = pthead("kop", "ser4")
head.initialize()

Is it really that hard to use the variable as an object (hope I get the terminology right)? I can hardly believe it is not a common thing to do, for example after user input...

I'm using python 2.7 (for legacy purposes).

• Rajan Chauhan: Use this head = pthead("kop", ser4) it will work.

Answer 1

You are not using it correctly. The port you are supplying isn't a port but a string `"ser4".

class pthead:
 def __init__(self, name, port):
 self.name = name
 self.port = port
 def initialize(self):
 self.port.write(initialization_commands) # it will work
if __name__ == "__main__":
 UART.setup("UART4")
 ser4 = serial.Serial(port="/dev/ttyO4", baudrate=9600, timeout=0.5)
 head = pthead("kop", ser4) #supplying port as second argument
 head.initialize()

• Dieter Vansteenwegen: That does indeed work when used in a script. In interactive mode (where I tried out different options), that wasn't the case... x = pthead("name", ser4) returns "NameError: name 'ser4' is not defined"
• Rajan Chauhan: @DieterVansteenwegenON4DD If you are using it as a script then you need to provide a port value of ser4 there.Since you want to supply your provide port you need to define it before in the code then pass it as an argument.
• Rajan Chauhan: The code outside the class is what you need to put in the other file while importing phead
• Dieter Vansteenwegen: Maybe I wasn't clear in my reply. It does work when I run it as a script, but if I start interactive mode, then from foo import pthead and try to create an instance with x = pthead("name", ser4) I get the "NameError: name 'ser4' is not defined"error if I do not put quotes around the port.
• Rajan Chauhan: @DieterVansteenwegenON4DD I got you but you haven't made your program like that you are supplying name and a port. You need to carryout changes either your __init__ function should take name and a port value as argument but here you are essentially using port variable as argument