Multiple classes in a single python file with different dependencies

Question

If we have multiple classes in a single Python file, is it possible to import modules or libraries independently in those classes?

I have found that unlike Java, Python has no style guide that suggests to separate classes in individual files. Even the Python modules have multiple classes; for example the calendar module has 10 classes in a single file (calendar module source code).

In my scenario, I have a Python file called planet.py. It has multiple classes. One of the classes requires to import pyttsx3 module. Then it needs to get a reference to the pyttsx3.Engine instance before using it. Currently I am importing the module and creating the instance in class __init__ method like below.

class Animal:
    pass

class Speaker:    
    def __init__(self):        
        import pyttsx3
        self.engine = pyttsx3.init()
    def speak(self, text):
        self.engine.say(text)
        self.engine.runAndWait()

Some other programmers suggest me not to import modules inside functions. They said it will execute the import statement every time the function is called.

I do not know how to do so. Apart from the main question, what is the best practice to follow in scenarios like this?

Answer 1

Import statements should usually be at the top of a python file (convention). According to convention, you should group classes with similar intentions and requirements together in one file. When you import a library, all classes in the file can use them. If a certain class does not need similar imports, or needs a lot of libraries imported which other classes do not need, it should, technically, be in a different file, and the file can be imported and instantiated.

Import statements in functions won't do any harm (apart from a very minimal delay time if run repeatedly), although, as @Evert said, can be a pain to the user experience if they fail.