I'm trying to get to grips with a Python module I've installed called 'mido' for handling MIDI I/O.
The function mido.get_output_names should tell me what output ports are available, but, when I try to use it in the interactive interpreter, I get the following error(s):
Python 3.6.0 (v3.6.0:41df79263a11, Dec 23 2016, 07:18:10) [MSC v.1900 32 bit (Intel)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> from mido import *
>>> mido.get_output_names()
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
NameError: name 'mido' is not defined
>>> get_output_names()
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
NameError: name 'get_output_names' is not defined
>>>
I've seen other questions with similar issues, but the suggested solution seems to be to name the package before the call (in this case 'mido.') but as you can see that doesn't seem to make a difference here.
I've also tried putting the code in a .py file and interpreting/running that and I get the same error messages (for with and without the '.mido' respectively)
Can anyone help me work out what I've missed?
I've also tried from mido.port import * and calls to port.get_output_names() in as many combinations as I could think of, with similar equivalent NameError messages.
Looking at the __init__.py file of the mido module you can see that it prevents star * imports by setting __all__ to an empty list:
# Prevent splat import.
__all__ = []
__all__ is the list of names picked up by from mod import *, setting it to [] makes sure nothing gets imported.
it also sets a couple of additional functions (like get_output_names) in the module dictionary via use of the set_backend helper function.
So, either import mido directly and use get_output_names by prefixing the module name:
import mido
mido.get_output_names(...)
or, import the name from the module and use it directly:
from mido import get_output_names
get_output_names(...)
seems strange, maybe try this way:
import mido
then when calling functions from the package, use:
mido.get_output_names()
you can also import this way:
import mido as md
then:
md.get_output_names()
Also:
- try to get to the package directory, and have a look in the files
- try to get help from the package from terminal when imported:
import mido
help(mido)
Related
Test.py:
def test():
print("Hello World")
test()
When I run this using the interpreter (ctrl+shift+p > Python: Select Interpreter > target interpreter), it works.
If I then try to run the repl (ctrl+shift+p > Python: Start REPL), I see the repl started in the terminal:
PS C:\Development\personal\python\GettingStarted> & c:/Development/personal/python/GettingStarted/.venv/Scripts/python.exe
Python 3.8.3 (tags/v3.8.3:6f8c832, May 13 2020, 22:20:19) [MSC v.1925 32 bit (Intel)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>>
However, if I try to execute the defined method in the repl, I get an undefined error:
>>> test()
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
NameError: name 'test' is not defined
Correct way #1 to import and use:
>>> import test
Hello World
>>> test.test()
Hello World
Correct way #2 to import and use:
>>> from test import test
Hello World
>>> test()
Hello World
If you get an ImportError for both ways above, then you are running the Python REPL from the wrong directory.
It's a bit confusing that the filename and function name are the same.
Also it's a bit unusual that there is a call to test() at the end of the file (causing the function to be called at import time). Typically it's wrapped like if __name__ == '__main__': test() to avoid the call at import time, but make the call when run as a script from the command-line.
Import test doesn't work, because Python keywords are lowercase and case sensitive.
from test import Test doesn't work, because Python identifiers (e.g. function names) are case sensitive.
import Test may work on Windows (but not on macOS, Linux and many other operating systems), because filenames on Windows are case insensitive.
import test.py doesn't work, because it's not allowed to have the .py extension as part of the import module name.
import test from test doesn't work, because from ... must come before import ....
I need to import a single class (not the whole file) from a python file starting with number.
There was a topic on importing a whole module and it works, but can't find my way around this one.
(In python, how to import filename starts with a number)
Normally it would be:
from uni_class import Student
though the file is called 123_uni_class.
Tried different variations of
importlib.import_module("123_uni_class")
and
uni_class=__import__("123_uni_class")
Error:
from 123_uni_class import Student
^
SyntaxError: invalid decimal literal
importlib.import_module("123_uni_class") returns the module after importing it, you must give it a valid name in order to reuse it:
import importlib
my_uni_class = importlib.import_module("123_uni_class")
Then you can access your module under the name 'my_uni_class'.
This would be equivalent to import 123_uni_class as my_uni_class if 123_uni_class were valid in this context.
It works for me:
Python 3.6.8 (default, Feb 14 2019, 22:09:48)
[GCC 7.4.0] on cygwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import importlib
>>> importlib.import_module('123_a')
<module '123_a' from '/path/to/123_a.py'>
>>> __import__('123_a')
<module '123_a' from '/path/to/123_a.py'>
You would not see an actual syntax error containing the literal text "from 123_uni_class import ..." unless you actually have some source code containing that line.
If you must, you can also bypass the import system entirely by reading the contents of the file and exec()-ing them, possibly into a namespace you provide. For example:
mod = {}
with open('123_uni_class.py') as fobj:
exec(fobj.read(), mod)
Student = mod['Student']
This general technique is used, for example, to read config files written in Python and things like that. I would discourage it though for normal usage and suggest you just use a valid module name.
This question already has answers here:
from ... import OR import ... as for modules
(6 answers)
Closed 4 years ago.
I've always used from a import b but recently a team at work decided to move a module into a new namespace, and issued a warning notice telling people to replace import b with import a.b as b.
I've never used import as and the only documentation I can find seems to suggest it doesn't support import a.b as b, though clearly it does.
but is there actually a difference, and if so what?
As far as I know, correct me if I am wrong.
First, import a.b must import a module(a file) or a package(a directory contains __init__.py).
For example, you can import tornado.web as web but you cannot import flask.Flask as Flask as Flask is an object in package flask.
Second, import a.b also import the namespace a which from a import b won't. You can check it by globals().
So what's the influence? For example:
import tornado.web as web
Now you have access to namespace tornado, but you cannot access tornado.options even though tornado has this module. But as python's global package management, if you from tornado import options, you will not only get access to options but also add it to namespace tornado. So now you can also access options by tornado.options.
I am going to provide only a partial answer, and I will speculate a bit.
1) Sometimes I have observed that the second way works while the first does not. On my system:
Python 3.6.3 (default, Oct 3 2017, 21:45:48)
[GCC 7.2.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> from tensorflow import keras # <- this works
>>>
>>> import tensorflow.keras as K # <- this fails
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
ModuleNotFoundError: No module named 'tensorflow.keras'
>>>
2) I usually don't see a difference between these two approaches to importing. I haven't investigated WHY there is a difference with TensorFlow. It may have to do with what names are imported to the top level by the various TensorFlow subfolder init.py files (which are completely empty in most cases, but the one in ../dist_packages/tensorflow/python is pretty long).
This question already has answers here:
Use 'import module' or 'from module import'?
(23 answers)
Closed 5 years ago.
I use to think both are equal until I tried this:
$python
Python 2.7.13 (default, Dec 17 2016, 23:03:43)
[GCC 4.2.1 Compatible Apple LLVM 8.0.0 (clang-800.0.42.1)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import Tkinter
>>> root=Tk()
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
NameError: name 'Tk' is not defined
>>> from Tkinter import *
>>> root=Tk()
So what's the core difference between these 2 kinds of import that import everything from a module?
Thanks.
when you import x , it binds the name x to x object , It doesn't give you the direct access to any object that is your module, If you want access any object you need to specify like this
x.myfunction()
On the other side when you import using from x import * , It brings all the functionalities into your module, so instead of x.myfunction() you can access it directly
myfunction ()
for example lets suppose we have module example.py
def myfunction ():
print "foo"
Now we have the main script main.py , which make use of this module .
if you use simple import then you need to call myfunction() like this
import example
example.myfucntion()
if you use from, you dont need to use module name to refer function , you can call directly like this
from example import myfunction
myfunction()
Here is the code I have:
import pickle
alist = ['here', 'there']
c = open('config.pck', 'w')
pickle.dump(alist, c)
and this is the error I receive:
Traceback (most recent call last):
File "C:\pickle.py", line 1, in ?
import pickle
File "C:\pickle.py", line 6, in ?
pickle.dump(alist, c)
AttributeError: 'module' object has no attribute 'dump'
whats going on? I am using python 2.4 on windows xp
Don't call your file pickle.py. It conflicts with the python standard libary module of the same name. So your import pickle is not picking up the python module.
The code you have works fine for me.
Python 2.5.4 (r254:67916, Dec 23 2008, 15:10:54) [MSC v.1310 32 bit (Intel)] on
win32
Type "help", "copyright", "credits" or "license" for more information.
>>> import pickle
>>>
>>> alist = ['here', 'there']
>>> c = open('config.pck', 'w')
>>>
>>> pickle.dump(alist, c)
>>>
The issue is that your filename "pickle.py" is making the import pickle statement try to import from your own file instead of the main library. Rename your code file.
Your script is called pickle and therefore shadows the module picke from the standard library. It imports itself and tries to call its dump function (and of course it doesn't have one).
Note that you're "lucky" that you don't get kicked into an infinite import loop (because importing the same module twice just creates another reference to the same module object in memory).