Multiple classes in a Python module
Question:
I’m very new to Python (I’m coming from a JAVA background) and I’m wondering if anyone could help me with some of the Python standards. Is it a normal or “proper” practice to put multiple class in a module? I have been working with Django and started with the tutorials and they place their database model classes in the same module. Is this something that is normally done or should I stick with 1 class per module? Is there a reason I would do one over the other?
Hope I’m being clear and not to generic. Thanks to everyone in advance!
Answers:
It is absolutely proper to do so. A module groups related functionality. If that functionality is implemented in several classes (e.g., Tree, Node, Leaf) then it is appropriate to place them together.
A module is more closely associated with a Java package than a Java class. You can also implement a module as a folder, named for the module, with an __init__.py file inside (so Python can identify the module as such; the __init__.py may also optionally include initialization code and lists of classes, functions, and sub-packages to export.)
It is certainly a normal thing to do in Python. When and why you choose one over the other is partly a matter of taste, and partly convention.
If you’re still getting to know Python, and therefore its conventions, reading the style guide is well worth your time.
When in doubt, just look at Python’s standard libraries 🙂
For example, the standard calendar module contains 31 classes. So yes, it is ok.
Here is a useful rule of thumb from what I have seen of typical Java projects:
The bottom-most package in Java should be a file in Python
What does that mean?
If your Java project was organized:
toplevel/
subproject/
Foo.java
Bar.java
subproject2/
Baz.java
Qux.java
Then your Python project should look like:
toplevel/
subproject.py <-- put class Foo, Bar here
subproject2.py <-- put class Baz, Qux here
Things to notice re: organization:
- Do not use inner classes. Just put
classes in the same module
- By convention, things that start with _ are “private”
- It’s OK to have “public variables”
Think it this way.
In java what you write is a Class where in the case of Python, you write a module instead of a class. So a module can contain several classes.
Whenever you want to use a particular class, import the respective module first and then call the class to make objects.
Here’s an example.
Classes.py (This is a module named ‘Classes’)
class MyClass(object):
def greet(self):
print("Hello World")
class MyNextClass(object):
def greetAgain(self):
print("Hello again")
Now I can import this module from anywhere I wish
import Classes
if __name__ == '__main__':
a=Classes.MyClass()
a.greet()
b=Classes.MyNextClass()
b.greetAgain()
I’m very new to Python (I’m coming from a JAVA background) and I’m wondering if anyone could help me with some of the Python standards. Is it a normal or “proper” practice to put multiple class in a module? I have been working with Django and started with the tutorials and they place their database model classes in the same module. Is this something that is normally done or should I stick with 1 class per module? Is there a reason I would do one over the other?
Hope I’m being clear and not to generic. Thanks to everyone in advance!
It is absolutely proper to do so. A module groups related functionality. If that functionality is implemented in several classes (e.g., Tree, Node, Leaf) then it is appropriate to place them together.
A module is more closely associated with a Java package than a Java class. You can also implement a module as a folder, named for the module, with an __init__.py file inside (so Python can identify the module as such; the __init__.py may also optionally include initialization code and lists of classes, functions, and sub-packages to export.)
It is certainly a normal thing to do in Python. When and why you choose one over the other is partly a matter of taste, and partly convention.
If you’re still getting to know Python, and therefore its conventions, reading the style guide is well worth your time.
When in doubt, just look at Python’s standard libraries 🙂
For example, the standard calendar module contains 31 classes. So yes, it is ok.
Here is a useful rule of thumb from what I have seen of typical Java projects:
The bottom-most package in Java should be a file in Python
What does that mean?
If your Java project was organized:
toplevel/
subproject/
Foo.java
Bar.java
subproject2/
Baz.java
Qux.java
Then your Python project should look like:
toplevel/
subproject.py <-- put class Foo, Bar here
subproject2.py <-- put class Baz, Qux here
Things to notice re: organization:
- Do not use inner classes. Just put
classes in the same module - By convention, things that start with _ are “private”
- It’s OK to have “public variables”
Think it this way.
In java what you write is a Class where in the case of Python, you write a module instead of a class. So a module can contain several classes.
Whenever you want to use a particular class, import the respective module first and then call the class to make objects.
Here’s an example.
Classes.py (This is a module named ‘Classes’)
class MyClass(object):
def greet(self):
print("Hello World")
class MyNextClass(object):
def greetAgain(self):
print("Hello again")
Now I can import this module from anywhere I wish
import Classes
if __name__ == '__main__':
a=Classes.MyClass()
a.greet()
b=Classes.MyNextClass()
b.greetAgain()