I am trying to learn python i tried to import a class in another class but it is not working
Application.py:
class Application:
def example(self):
return "i am from Application class"
Main.py
class Main:
def main():
application = Application()
application.example()
if __name__ == "__main__":
Main.main()
This gives me :
File "Main.py", line 11, in <module>
Main.main()
TypeError: unbound method main() must be called with Main instance as first argument (got nothing instead)
The error has nothing to do with importing (Although you don't seem to import Application anywhere). The problem is that you use the main method like a static method without declaring it to be static.
To solve this, You either need to declare your main method as static or create an instance of the Main class.
As a static method (add the #staticmethod decorator):
class Main():
#staticmethod
def main():
...
With an Instance:
class Main():
def main(self):
....
if __name__ == "__main__":
myMain = Main() #create an instance
myMain.main() #call the function on the instance
Also, to import your Application class from Application.py, you would just write this:
from Application import Application
You should instantiate your Main class first.
if __name__ == '__main__':
myMain = Main()
myMain.main()
But this will give you another error:
TypeError: main() takes no arguments (1 given)
There are two ways to fix this. Either make Main.main take one argument:
class Main:
def main(self):
application = Application()
application.example()
or make Main.main a static method. In which case you don't have to instantiate your Main class:
class Main:
#staticmethod
def main():
application = Application()
application.example()
if __name__ == "__main__":
Main.main()
Related
I have a little problem, I have my code below.
I want to call the "speak" function with two arguments inside the main() class.
When I call speak it says that self its not defined, and i don't know how to make it work...
Any ideas?
class main():
def blueon(self):
print("teste")
def speak(self,fala):
self.blueon
print(fala)
speak("testeaaaaa")
Try something like this.
Comments explain changes
class Main: # Class name capitalized and no parenthesis if the class has no base classs
def __init__(self): # class constructor. Initialize here your variables
pass
# if you have a function that doesn't use self, you can declare it static
#staticmethod
def blueon():
print("teste")
def speak(self, fala):
self.blueon() # added missing parenthesis
print(fala)
if __name__ == "__main__": # add this so you can later import your class as a library without executing your test code
m = Main() # instantiate the class
m.speak("testeaaaaa") # call the speak method
You run speak() in wrong way.
First you have to create instance of class m = main() and later use m.speak("text").
And you have to do with different indetation.
BTW: There is good rule to use CamelCaseName for classes - class Main(): - it helps to recognize class in code, and it allows to do main = Main().
More in PEP 8 -- Style Guide for Python Code
# --- classes ---
class Main():
def blueon(self):
print("teste")
def speak(self, fala):
self.blueon() # you forgot `()
print(fala)
# --- main ---
main = Main()
main.speak("testeaaaaa")
I am going to attach two blocks of code, the first is the main code that is ran the second is the testClass file containing a sample class for testing purposes. To understand what's going on it's probably easiest to run the code on your own. When I call sC.cls.print2() it says that the self parameter is unfulfilled. Normally when working with classes, self (in this case) would be sC.cls and you wouldn't have to pass it as a parameter. Any advice is greatly appreciated on why this is occuring, I think it's something to do with exec's scope but even if I run this function in exec it gives the same error and I can't figure out a way around it. If you'd like any more info please just ask!
import testClass
def main():
inst = testClass.myClass()
classInfo = str(type(inst)).split()[1].split("'")[1].split('.')
print(classInfo)
class StoreClass:
def __init__(self):
pass
exec('from {} import {}'.format(classInfo[0], classInfo[1]))
sC = StoreClass()
exec('sC.cls = {}'.format(classInfo[1]))
print(sC.cls)
sC.cls.print2()
if __name__ == '__main__':
main()
class myClass:
def printSomething(self):
print('hello')
def print2(self):
print('hi')
I'm still in the learning phase and I have this question.
So in order to execute a class, we use if __name__ == '__main__': and call the class as the following
class Example():
def test(self):
print "Hello There"
if __name__ == '__main__':
Example()
However, I saw some classes that use def launch(): instead of if __name__ == '__main__':, so the question here: Are they similar so I can both ways or def launch(): has a special propose?
Thank you.
Python runs anything in the top level this is why we use classes and functions to separate jobs (among other reasons).
So for example here
Script a.py
def main():
pass
main()
The interpreter will define a function called main() but when it reaches the main() call in the top level (aligned left most)
it will execute the main function.
Now in the case of your launch()
if __name__ == '__main__':
Example()
vs
__name__ = __main__
This is used in the case where someone wants to import a program or class but doesn't want it to run when the interpreter runs into it.
Import a will call the main() at that point and time
however let's say b.py is structurally similar but instead of main() it has __name__ = __main__, b.py won't run unless directly called.
The reason I bring this is up is because as #harshil9968 pointed out, Python has no "launch" method. What likely was happening is they defined a launch() method instead of main()
Then put it under a class
class A():
def launch(self):
#actions
if __name__ == '__main__':
A()
Call to A() calls the launch() method within the A class.
I am trying to create a class called ListenerVilma that has two methods: "Clock_" and "Diagnostics_". Nevertheless both methods will call inner functions. The following code shows my attempt to achieve the mentioned behavior, but when I call ListenerVilma.Clock_() the get the following error:
TypeError: unbound method Clock_() must be called with ListenerVilma instance as first argument (got nothing instead)
How should a create my class ListenerVilma???
Thanks.
#!/usr/bin/env python
import rospy
from rosgraph_msgs.msg import Clock
from diagnostic_msgs.msg import DiagnosticArray
class ListenerVilma:
"""Class that listens all topics of the file vilmafeagri"""
def Clock_(self):
"""Method that listens the topic /clock if the file vilmafeagri"""
def __init__(self):
self.listener()
def callback(self, clock):
print clock
def listener(self):
rospy.Subscriber('clock', Clock, self.callback)
def Diagnostics_(self):
"""Method that listen the topic /diagnostics from rosbag file vilmafeagri"""
def __init__(self):
self.listener()
def callback(self, diagnostics):
print diagnostics
def listener(self):
rospy.Subscriber('diagnostics', DiagnosticArray, self.callback)
if __name__ == '__main__':
rospy.init_node('listener', anonymous=True)
ListenerVilma.Clock_()
rospy.spin()
the error is in line 41 in ListenerVilma.Clock_() here your directly using the method of your class so no implicit argument is pass and a instance of ListenerVilma is expected. The solution is ListenerVilma().Clock_() this first create a instance of your class and from say instance call its Clock_ method.
Outside that, your class construction is very weird, the __init__ is used to initialize a class and a basic class construction is like this
class Foo:
"""example class"""
def __init__(self,*argv,**karg):
"""initialize this class"""
#do something with argv and/or karg according to the needs
#for example this
print "init argv", argv
print "init karg", karg
self.ultimate=42
def do_stuff(self):
"""this method do something"""
print "I am doing some stuff"
print "after 7.5 million years of calculations The Answer to the Ultimate Question of Life, the Universe, and Everything is: ", self.ultimate
def do_some_other_stuff(self,*argv,**karv):
"""this method do something else"""
print "method argv", argv
print "method karg", karg
# basic usage
test = Foo(1,2,3,key_test=23)
test.do_stuff()
test.do_some_other_stuff(7,8,9,something=32)
test.ultimate = 420
test.do_stuff()
I am not quite sure what you intentions are, but you build Clock_ and Diagnostics_ as a class, but they are not, and as right now they do nothing, if you want they to be class on their own do
class Clock_:
def __init__(self):
self.listener()
def callback(self, clock):
print clock
def listener(self):
rospy.Subscriber('clock', Clock, self.callback)
and the same with Diagnostics_, and I don't see a reason to the listener method so I would put what it does in the __init__, but maybe the rospy need it? I don't know, but for the looks of it then it should be used as
rospy.init_node('listener', anonymous=True)
Clock_()
Diagnostics_()
rospy.spin()
The Clock_ method doesn't belong to the class; it's an 'instance' method.
There are two options
In the main function: create an instance of ListenerVilma: listener = ListenerVilma(), or
In the ListenerVilma class: annotate the methods with #classmethod and make the class inherit from object: class ListenerVilma(object):. But remember, the first argument in your methods will be a reference to the class and not a reference to an instance.
The following code performs better the behavior that I wanted. :)
class ListenerVilma:
def CLOCK(self):
def clock_sub():
rospy.Subscriber('clock', Clock, clock_callback)
def clock_callback(clock):
print clock
clock_sub()
def DIAGNOSTICS(self):
def diagnostics_sub():
rospy.Subscriber('diagnostics', DiagnosticArray, diagnostics_callback)
def diagnostics_callback(diagnostics):
print diagnostics
diagnostics_sub()
if __name__ == '__main__':
rospy.init_node('listener', anonymous=True)
myVilma = ListenerVilma()
myVilma.CLOCK()
myVilma.DIAGNOSTICS()
rospy.spin()
I have two files, one of the test.py is
import new.py
class Test:
def __init__(self):
return
def run(self):
return 1
if __name__ == "__main__":
one=Test()
one.run()
and new.py
class New:
def __init__(self):
one.run()
New()
Now when i run python test.py I get this error,
Traceback (most recent call last):
File "test.py", line 1, in <module>
import new.py
File "/home/phanindra/Desktop/new.py", line 5, in <module>
New()
File "/home/phanindra/Desktop/new.py", line 3, in __init__
one.run()
NameError: global name 'one' is not defined
But I want to use this instance of one in my New!!
Can I do this??
edit:
I want to access the variable in test.py in new.py to do some process and give them back to test.py. Isn't this possible?
If you want your New class to use the instance of Test you created, you have to pass it in as part of the constructor.
new.py
class New:
def __init__(self, one):
one.run()
test.py
import new
class Test:
def __init__(self):
return
def run(self):
return 1
if __name__ == "__main__":
one=Test()
two = new.New(one);
Playing around with globals is a great way to break your code without realizing how you did it. It is better to explicitly pass in the reference you want to use.
No, you can't. The closest you can get is to pass the thing you need in to the constructor:
class New(object):
def __init__(self, one):
one.run()
one is defined inside the if __name__=='__main__' block.
Consequently, one will get defined only if test.py is run as a script (rather than imported).
For the module new to access one from the test module, you'll need to pull one out of the if __name__ block:
test.py:
class Test:
def __init__(self):
return
def run(self):
return 1
one=Test()
if __name__ == "__main__":
one.run()
Then access one by the qualified name test.one:
new.py:
import test
class New:
def __init__(self):
test.one.run()
New()