For larger programs, in order to be more organized, I have been looking into dividing my code up into different .py files and having the main file that calls upon those files when needed. I have looked around and seen lots of remarks about creating a directory and a SystemPath for Python. Are those reasonable options for a program that could be distributed between a few computers? As a test, I tried to assemble an example:
This is the class named grades in the same directory as main
class student:
def __init__(self):
self.name = ""
self.score = 0
self.grade = 0
def update(self,name,score,grade):
self.score = score
self.name = name
self.grade = grade
print self.score,self.name,self.grade
s = student()
s.update(name,score,grade)
This is my main script currently:
from grades import score
import random
name = 'carl'
score = random.randrange(0,100)
grade = 11
s = student()
s.score(name,score,grade)
There are some questions I have generally about this method:
Is there a way to import all from different files or do I need to specify each individual class?
If I just had a function, is it possible to import it just as a function or can you only import via a class?
Why is it when I call upon a class, in general, I have to make a variable for it as in the example below?
# way that works
s = student()
s.update(name,score,grade)
# incorrect way
student.update(name,score,grade)
Thank you for your time and thought towards my question.
Yes.
You can import instance of student from other script to main script like this:
from grades import s
# if your first script is called grades.py
import random
name = 'carl'
score = random.randrange(0,100)
grade = 11
# you can directly use it without initializing it again.
s.score(name,score,grade)
2.
If you have a function called test() in grades.py, you can import it in this way:
from grades import test
# then invoke it
test()
3.
This variable stands for the instance of class student. You need this instance to invoke the function inside.
Generally, to divide the source code of a program, Python use module to do that, which corresponds to a *.py file. Then for your 3 questions:
You can import a whole "module content" (function, class, global variables, ...) through import module_name.*
for a function, if it is a function in a class(member method, class method or static method) you can not only import the function, you should import class to use the method; if it is a function under module, you can separately import the function through import module_name.function_name
update is a member function of the student class, so you should use it through an instance. if it is a class method or static method, you can use it through the class name you wrote.
1: Is there a way to import all from different file or do i need to
specify each individual class?
You can use the "wildcard import", but you probably shouldn't. See
Should wildcard import be avoided?
If i just had a function, is it possible to import it just as a
function or can you only import via a class?
Functions can be totally independent of classes in Python.
3.Why is it when i call upon a class in general i have to make a variable for it as in the example below?
You should read up on object-oriented programming. In the basic cases, you have to instantiate instances of a class in order to use that class's functionality. In your example, the class student describes what it means to be a student, and the statement
s = student()
creates a student and names it "s".
I think this should be clear after reading a bit about object-oriented programming.
First, you can use from module import * to import everything like:
hello.py:
def hello():
print 'hello'
def bye():
print 'Bye'
main.py:
from hello import *
hello()
bye()
But it's not a good way, if you have two files, two functions have the same name,
so use
from hello import hello, bye
hello()
bye()
is better, it an example for function ,as same as class.
Third before Second, student is a class, so you have to use an instance object to use the function which with self parameter. If you want to use student.function, the function must be a static method like this:
class Person:
def __init__():
pass
#staticmethod
def Count():
return 1
print Person.Count()
Second, you can import the function in a class file which is independent of the class.
Is there a way to import all from different file or do i need to specify each individual class?
the answer is yes , as python import statement use sys.path (A list of strings that specifies the search path for modules ) you need to add the patht of your modules in sys.path , for example if you want to interact between different computers you can put your modules in public folder and add the path of folder to sys.path :
import sys
sys.path.append( path to public )
If i just had a function, is it possible to import it just as a function or can you only import via a class?
you just need to use from ... import function_name.
Why is it when i call upon a class in general i have to make a variable for it as in the example below?
for this question you just need to read the python Class objects documentation :
Class objects support two kinds of operations: attribute references and instantiation.
Related
How can I avoid a global variable when creating an object? Someone told me that when I create the objects, it is considered doing that globally.
For instance if I have my class like this
class Windpower(object):
def __init__(self,name):
self.name=name
def calc_area(self,dia):
area=((dia/2)**2*math.pi)
return area
def calc_wind_energy(self,area,v):
energy=(random.uniform(0.10,0.4)*1.2*area*v**3*0.5)
return energy
def get_velocity(self):
with open('smhi.txt') as input:
smhi_list=[int(line.strip()) for line in input if line.strip()]
return smhi_list
windpower = Windpower("Stockholm")
solarpower=Solarpower(500,4)
Main.py
def average(lat):
energy_list = [] #
table = [] #
area = klass.solarpower.area
sundigit=klass.solarpower.sundigit
This is more of an anti-pattern in python than anything else. The act of having executable code on the module level should be avoided, because this can be executed when the module is being imported by other modules.
There are however cases to place code on the module level, such as providing objects on the module as part of your API (think Singleton), or doing any module initialization.
If you need this code to be executed only when you run the module as the main program you should place them under
if __name__ == '__main__':
windpower = Windpower("Stockholm")
solarpower=Solarpower(500,4)
Or put them in a function.
Bear in mind that the term "global" is incorrect here, as these objects are scoped within the module they're defined in, rather than the whole executable program.
When you instantiate your objects in the top level of the module (a python file), as you do in the example code you gave, they're accessible from the root of the module.
However, you really should instantiate them in the module where you use them. Here's an example:
wind.py
class WindPower(object):
def __init__(self,name):
self.name=name
main.py
import wind
city = wind.WindPower("Stockholm")
velocity = city.get_velocity()
I have a file named schedule.py:
class SchedGen:
""" Class creates a pseudo random Schedule.
With 3/4 of total credit point required for graduation"""
def __init__(self, nof_courses=40):
random.seed()
self.courses = {}
self.nof_courses = nof_courses
for i in xrange(nof_courses):
self.courses[i] = college.Course(i)
self.set_rand_cred()
self.set_rand_chance()
self.set_rand_preq_courses()
def set_rand_cred(self):
""" Set random credit to courses uniformly between 2 and 6"""
temp_dict = self.courses.copy()
While importing content of schedule do I do import schedule like:
import schedule
If that's correct how can I access the function set_rand_cred(self) from SchedGen class?
You can either do
import schedule
schedgen = schedule.SchedGen()
schedgen.set_rand_red()
or
from schedule import SchedGen
schedgen = SchedGen()
schedgen.set_rand_red()
This link provides some information how Pythons import statement works.
The set_rand_cred() function is an instance function of the class, so you need to first create a class instance. To create a class instance, you need to be able to access the name of the class. You can do that in two ways.
Here's how to solve the problem using each way:
Importing the module:
import schedule
s = schedule.SchedGen()
s.set_rand_cred()
Importing the class from within the module and putting the class into the local namespace:
from schedule import SchedGen
s = SchedGen()
s.set_rand_cred()
You'd have to first make an instance (using the class's qualified name), then access that function as an attribute of the instance:
import schedule
s = schedule.SchedGen()
s.set_rand_cred()
Like that:
import schedule
schedule_generator = schedule.SchedGen()
schedule_generator.set_rand_cred()
For more information read the Python documentation: http://docs.python.org/2/tutorial/classes.html
That's exactly how you import another module, whether it be third-party or one that you created. Now, one great thing about python is the many ways you can go with this. One being, importing the module, retrieving the class from that, or importing the class by itself.
import schedule
foo = schedule.SchedGen()
returned_var = foo.set_rand_cred()
If you import the class by itself, it's almost exactly the same:
from schedule import SchedGen
foo = SchedGen()
returned_var = foo.set_rand_cred()
You can do this:
import schedule
schedule.SchedGen.set_rand_cred()
But it's more common to do this:
from schedule import SchedGen
SchedGen.set_rand_cred()
I'm developing a PyQT4 application, and it's getting pretty hard for me to navigate through all of the code at once. I know of the import foo statement, but I can't figure out how to make it import a chunk of code directly into my script, like the BASH source foo statement.
I'm trying to do this:
# File 'functions.py'
class foo(asd.fgh):
def __init__(self):
print 'foo'
Here is the second file.
# File 'main.py'
import functions
class foo(asd.fgh):
def qwerty(self):
print 'qwerty'
I want to include code or merge class decelerations from two separate files. In PHP, there is import_once('foo.php'), and as I mentioned previously, BASH has source 'foo.sh', but can I accomplish this with Python?
Thanks!
For some reason, my first thought was multiple inheritance. But why not try normal inheritance?
class foo(functions.foo):
# All of the methods that you want to add go here.
Is there some reason that this wont work?
Since you just want to merge class definitions, why don't you do:
# main.py
import functions
# All of the old stuff that was in main.foo is now in this class
class fooBase(asd.fgh):
def qwerty(self):
print 'qwerty'
# Now create a class that has methods and attributes of both classes
class foo(FooBase, functions.foo): # Methods from FooBase take precedence
pass
or
class foo(functions.foo, FooBase): # Methods from functions.foo take precedence
pass
This takes advantage of pythons capability for multiple inheritance to create a new class with methods from both sources.
You want execfile(). Although you really don't, since redefining a class, uh... redefines it.
monkey patching in python doesn't work in nearly the same way. This is normally considered poor form, but if you want to do it anyways, you can do this:
# File 'functions.py'
class foo(asd.fgh):
def __init__(self):
print 'foo'
the imported module remains unchanged. In the importing module, we do things quite differently.
# File 'main.py'
import functions
def qwerty(self):
print 'qwerty'
functions.foo.qwerty = qwerty
Note that there is no additional class definition, just a bare function. we then add the function as an attribute of the class.
I have 2 classes:
import follow
class User(object):
def __init__(self):
pass
import user
class Follow(object):
def doSomething(self):
u = User()
>> f = Follow()
>> f.doSomething()
>> NameError: global name 'User' is not defined
Is this causing a problem because both classes import each other? Is there the equivalent of an import once? Any other potential causes? Thanks.
u = user.User()
or, alternatively:
from user import User
u = User()
user.py
class User(object):
def __init__(self):
pass
follow.py
from user import User
class Follow(object):
def doSomething(self):
u = User()
The problem seems to be that you're are importing user and then accessing User. Use user.User or (not as nice) from user import User.
Python treats modules as namespaces and so anything defined in the global scope of a module is only available as an attribute of the module in other namespaces that import it. There is no true 'global scope' in Python the way there is in some other languages.
The from foo import bar syntax allows one to bring an identifier directly into whatever scope it is executed in but later attempts to reload the module will no longer update that reference. There is also the problem of keeping track of where identifiers come from.
Also, you don't actually seem to be using follow in the user module. This shouldn't be a problem but if you are actually using it, then you should probably extend your example to include the use. How modules import each other can determine if this is actually allowed or not.
You can try to use either
from user import *
(which is usually not recommended)
or create User objects using qualified name:
...
u = user.User()
Correct import
from user import User
doesn't work in your case, I guess, because of recursive imports.
There will always be a problem no matter.
If this a theoretical question then fine.
But if this an actual design then stop. following is an action. It should be a function in the class User to make any sence.
class User(object):
def __init__(self):
print "bleh"
def follow(self,otheruser)
following.append(otheruser)
this makes much more sense. following obviously is a list pulled from somewhere either a variable or directly from the database.
What are the best practices for extending an existing Python module – in this case, I want to extend the python-twitter package by adding new methods to the base API class.
I've looked at tweepy, and I like that as well; I just find python-twitter easier to understand and extend with the functionality I want.
I have the methods written already – I'm trying to figure out the most Pythonic and least disruptive way to add them into the python-twitter package module, without changing this modules’ core.
A few ways.
The easy way:
Don't extend the module, extend the classes.
exttwitter.py
import twitter
class Api(twitter.Api):
pass
# override/add any functions here.
Downside : Every class in twitter must be in exttwitter.py, even if it's just a stub (as above)
A harder (possibly un-pythonic) way:
Import * from python-twitter into a module that you then extend.
For instance :
basemodule.py
class Ball():
def __init__(self,a):
self.a=a
def __repr__(self):
return "Ball(%s)" % self.a
def makeBall(a):
return Ball(a)
def override():
print "OVERRIDE ONE"
def dontoverride():
print "THIS WILL BE PRESERVED"
extmodule.py
from basemodule import *
import basemodule
def makeBalls(a,b):
foo = makeBall(a)
bar = makeBall(b)
print foo,bar
def override():
print "OVERRIDE TWO"
def dontoverride():
basemodule.dontoverride()
print "THIS WAS PRESERVED"
runscript.py
import extmodule
#code is in extended module
print extmodule.makeBalls(1,2)
#returns Ball(1) Ball(2)
#code is in base module
print extmodule.makeBall(1)
#returns Ball(1)
#function from extended module overwrites base module
extmodule.override()
#returns OVERRIDE TWO
#function from extended module calls base module first
extmodule.dontoverride()
#returns THIS WILL BE PRESERVED\nTHIS WAS PRESERVED
I'm not sure if the double import in extmodule.py is pythonic - you could remove it, but then you don't handle the usecase of wanting to extend a function that was in the namespace of basemodule.
As far as extended classes, just create a new API(basemodule.API) class to extend the Twitter API module.
Don't add them to the module. Subclass the classes you want to extend and use your subclasses in your own module, not changing the original stuff at all.
Here’s how you can directly manipulate the module list at runtime – spoiler alert: you get the module type from types module:
from __future__ import print_function
import sys
import types
import typing as tx
def modulize(namespace: tx.Dict[str, tx.Any],
modulename: str,
moduledocs: tx.Optional[str] = None) -> types.ModuleType:
""" Convert a dictionary mapping into a legit Python module """
# Create a new module with a trivially namespaced name:
namespacedname: str = f'__dynamic_modules__.{modulename}'
module = types.ModuleType(namespacedname, moduledocs)
module.__dict__.update(namespace)
# Inspect the new module:
name: str = module.__name__
doc: tx.Optional[str] = module.__doc__
contents: str = ", ".join(sorted(module.__dict__.keys()))
print(f"Module name: {name}")
print(f"Module contents: {contents}")
if doc:
print(f"Module docstring: {doc}")
# Add to sys.modules, as per import machinery:
sys.modules.update({ modulename : module })
# Return the new module instance:
return module
… you could then use such a function like so:
ns = {
'func' : lambda: print("Yo Dogg"), # these can also be normal non-lambda funcs
'otherfunc' : lambda string=None: print(string or 'no dogg.'),
'__all__' : ('func', 'otherfunc'),
'__dir__' : lambda: ['func', 'otherfunc'] # usually this’d reference __all__
}
modulize(ns, 'wat', "WHAT THE HELL PEOPLE")
import wat
# Call module functions:
wat.func()
wat.otherfunc("Oh, Dogg!")
# Inspect module:
contents = ", ".join(sorted(wat.__dict__.keys()))
print(f"Imported module name: {wat.__name__}")
print(f"Imported module contents: {contents}")
print(f"Imported module docstring: {wat.__doc__}")
… You could also create your own module subclass, by specifying types.ModuleType as the ancestor of your newly declared class, of course; I have never personally found this necessary to do.
(Also, you don’t have to get the module type from the types module – you can always just do something like ModuleType = type(os) after importing os – I specifically pointed out this one source of the type because it is non-obvious; unlike many of its other builtin types, Python doesn’t offer up access to the module type in the global namespace.)
The real action is in the sys.modules dict, where (if you are appropriately intrepid) you can replace existing modules as well as adding your new ones.
Say you have an older module called mod that you use like this:
import mod
obj = mod.Object()
obj.method()
mod.function()
# and so on...
And you want to extend it, without replacing it for your users. Easily done. You can give your new module a different name, newmod.py or place it by same name at a deeper path and keep the same name, e.g. /path/to/mod.py. Then your users can import it in either of these ways:
import newmod as mod # e.g. import unittest2 as unittest idiom from Python 2.6
or
from path.to import mod # useful in a large code-base
In your module, you'll want to make all the old names available:
from mod import *
or explicitly name every name you import:
from mod import Object, function, name2, name3, name4, name5, name6, name7, name8, name9, name10, name11, name12, name13, name14, name15, name16, name17, name18, name19, name20, name21, name22, name23, name24, name25, name26, name27, name28, name29, name30, name31, name32, name33, name34, name35, name36, name37, name38, name39
I think the import * will be more maintainable for this use-case - if the base module expands functionality, you'll seamlessly keep up (though you might shade new objects with the same name).
If the mod you are extending has a decent __all__, it will restrict the names imported.
You should also declare an __all__ and extend it with the extended module's __all__.
import mod
__all__ = ['NewObject', 'newfunction']
__all__ += mod.__all__
# if it doesn't have an __all__, maybe it's not good enough to extend
# but it could be relying on the convention of import * not importing
# names prefixed with underscores, (_like _this)
Then extend the objects and functionality as you normally would.
class NewObject(object):
def newmethod(self):
"""this method extends Object"""
def newfunction():
"""this function builds on mod's functionality"""
If the new objects provide functionality you intend to replace (or perhaps you are backporting the new functionality into an older code base) you can overwrite the names
May I suggest not to reinvent the Wheel here? I'm building a >6k line Twitter Client for 2 month now, at first I checked python-twitter too, but it's lagging a lot behind the recent API changes,, Development doesn't seem to be that active either, also there was(at least when I last checked) no support for OAuth/xAuth).
So after searching around a bit more I discovered tweepy:
http://github.com/joshthecoder/tweepy
Pros: Active development, OAauth/xAuth and up to date with the API.
Chances are high that what you need is already in there.
So I suggest going with that, it's working for me, the only thing I had to add was xAuth(that got merge back to tweepy :)
Oh an a shameless plug, if you need to parse Tweets and/or format them to HTML use my python version of the twitter-text-* libraries:
http://github.com/BonsaiDen/twitter-text-python
This thing is unittestetd an guaranteed to parse Tweets just like Twitter.com does it.
Define a new class, and instead of inherit it from the class you want to extend from the original module, add an instance of the original class as an attribute to your new class.
And here comes the trick: intercept all non-existing method calls on your new class and try to call it on the instance of the old class.
In your NewClass just define new or overridden methods as you like:
import originalmodule
class NewClass:
def __init__(self, *args, **kwargs):
self.old_class_instance = originalmodule.create_oldclass_instance(*args, **kwargs)
def __getattr__(self, methodname):
"""This is a wrapper for the original OldClass class.
If the called method is not part of this NewClass class,
the call will be intercepted and replaced by the method
in the original OldClass instance.
"""
def wrapper(*args, **kwargs):
return getattr(self.old_class_instance, methodname)(*args, **kwargs)
return wrapper
def new_method(self, arg1):
"""Does stuff with the OldClass instance"""
thing = self.old_class_instance.get_somelist(arg1)
# returns the first element only
return thing[0]
def overridden_method(self):
"""Overrides an existing method, if OldClass has a method with the same name"""
print("This message is coming from the NewClass and not from the OldClass")
In my case I used this solution when simple inheritance from the old class was not possible, because an instance had to be created not by its constructor, but with an init script from an other class/module. (It is the originalmodule.create_oldclass_instance in the example above.)