I know this could be caused by having a self-defined python file called random.py. I have searched for it, there is not file with such names, also there are no "pyc" file with this name.
I've also tried it by just typing the command in the terminal, and it seems to work! But it doesnt work when I try to compile the file!
Any idea what the problem might be?
Thanks!
import csv
import random
from numpy import *
from scipy.stats import norm
....
index = random.randrange(length)
...
First, you shouldn't do this on general principles:
from numpy import *
That shadows many built-ins like any and all with numpy versions which behave very differently. But in this case, it's also causing your other problem, because there's a numpy.random which is shadowing the main random module:
>>> import random
>>> random
<module 'random' from '/usr/lib/python3.4/random.py'>
>>> from numpy import *
>>> random
<module 'numpy.random' from '/usr/local/lib/python3.4/dist-packages/numpy/random/__init__.py'>
Note as an aside that if you're going to be generating many random numbers, using np.random instead of random is likely to be faster. (import numpy as np is the standard character-saving alias.)
It is not a best practice to import everything from modules. In this case, numpy seems to be interfering with random. When I change
from numpy import *
to
import numpy
the script runs. This would require you to reference anything you are using from numpy in the intervening code.
Related
I have a script which is importing lots of packages, including import numpy as np.
I have lots of scripts which need to import all of these packages (including some of my own). To make my life easier, I have a file called mysetup.py in my path to import all the packages. It includes the statement in a function called "import numpy as np".
I run "main.py". It runs the following
from mysetup import *
import_my_stuff()
np.pi()
"mysetup.py"
def import_my_stuff():
import numpy as np
return
However, I am unable to use numpy in "main.py" - this code will fail. Any suggestions as to why?
The problem you are facing is a consequence of a very important features of Python: namespaces.
https://docs.python.org/3/tutorial/classes.html#python-scopes-and-namespaces
https://realpython.com/python-namespaces-scope/
Basically, in your case, when you do that (numpy) import inside the (import_my_stuff) function, you are defining the code object numpy/np inside the function namespace. (scope, if you prefer).
To solve your issue (the way you are doing; not the only way), you should simply import everything at the module top level (without a function encapsulating the imports):
mysetup.py:
import numpy as np
# other modules...
main.py:
from mysetup import *
np.pi()
Imports in functions are not the best idea.
But you can just define whatever imports you need in top level code of mysetup.py
import numpy as np
and then it will be available when you import * from mysetup
from mysetup import *
print(np.pi)
Aloha!
I have two blocks of code, one that will work and one that will not. The only difference is a commented line of code for a numpy module I don't use. Why am I required to import that model when I never reference "npm"?
This command works:
import numpy as np
import numpy.matlib as npm
V = np.array([[1,2,3],[4,5,6],[7,8,9]])
P1 = np.matlib.identity(V.shape[1], dtype=int)
P1
This command doesn't work:
import numpy as np
#import numpy.matlib as npm
V = np.array([[1,2,3],[4,5,6],[7,8,9]])
P1 = np.matlib.identity(V.shape[1], dtype=int)
P1
The above gets this error:
AttributeError: 'module' object has no attribute 'matlib'
Thanks in advance!
Short Answer
This is because numpy.matlib is an optional sub-package of numpy that must be imported separately.
The reason for this feature may be:
In particular for numpy, the numpy.matlib sub-module redefines numpy's functions to return matrices instead of ndarrays, an optional feature that many may not want
More generally, to load the parent module without loading a potentially slow-to-load module which many users may not often need
Possibly, namespace separation
When you import just numpy without the sub-package matlib, then Python will be looking for .matlib as an attribute of the numpy package. This attribute has not been assigned to numpy without importing numpy.matlib (see discussion below)
Sub-Modules and Binding
If you're wondering why np.matlib.identity works without having to use the keyword npm, that's because when you import the sub-module matlib, the parent module numpy (named np in your case) will be given an attribute matlib which is bound to the sub-module. This only works if you first define numpy.
From the reference:
When a submodule is loaded using any mechanism (e.g. importlib APIs, the import or import-from statements, or built-in import()) a binding is placed in the parent module’s namespace to the submodule object.
Importing and __init__.py
The choice of what to import is determined in the modules' respective __init__.py files in the module directory. You can use the dir() function to see what names the respective modules define.
>> import numpy
>> 'matlib' in dir(numpy)
# False
>> import numpy.matlib
>> 'matlib' in dir(numpy)
# True
Alternatively, if you look directly at the __init__.py file for numpy you'll see there's no import for matlib.
Namespace across Sub-Modules
If you're wondering how the namespace is copied over smoothly;
The matlib source code runs this command to copy over the numpy namespace:
import numpy as np # (1)
...
# need * as we're copying the numpy namespace
from numpy import * # (2)
...
__all__ = np.__all__[:] # copy numpy namespace # (3)
Line (2), from numpy import * is particularly important. Because of this, you'll notice that if you just import numpy.matlib you can still use all of numpy modules without having to import numpy!
Without line (2), the namespace copy in line (3) would only be attached to the sub-module. Interestingly, you can still do a funny command like this because of line (3).
import numpy.matlib
numpy.matlib.np.matlib.np.array([1,1])
This is because the np.__all__ is attached to the np of numpy.matlib (which was imported via line (1)).
You never use npm but you do use np.matlib, so you could change your 2nd import line to just:
import numpy.matlib
Or you could keep your 2nd import line as is but instead use:
P1 = npm.identity(V.shape[1], dtype=int)
Is there are reason you don't use np.identity?
P1 = np.identity(V.shape[1], dtype=int)
This module contains all functions in the numpy namespace, with the following replacement functions that return matrices instead of ndarrays.
Unless you are wedded to 2d np.matrix subclass, you are better off sticking with the regular ndarray versions.
(Others have pointed out that the import why is based on the __init__ specs for numpy. numpy imports most, but not all of its submodules. The ones it does not automatically import are used less often. It's a polite way of saying, You don't really need this module)
new to Python programming and have encountered an issue importing modules.
I have a main application (compare.py) with imports as follows :
# import the necessary packages
from skimage.measure import structural_similarity as ssim
import matplotlib.pyplot as plt
import numpy as np
import os
import skimage
from skimage import io
from skimage import color
from epilib import mse
from epilib import compare_images
and I have defined two functions in epilib, one called mse() and one called compare_images().
The code in mse() requires numpy. When I execute 'python compare.py', I get the following error message :
File "C:\Users\Dan\epilib.py", line 7, in mse err = np.sum((imageA.astype("float") - imageB.astype("float")) ** 2)
NameError: name 'np' is not defined
I assumed that because 'import numpy as np' was executed prior to import epilib, that the numpy library would be available to epilib? When I added 'import numpy as np' to the top of epilib, the issue resolved.
I don't see it as very efficient to have to move all the import statements to epilib. I was hoping to have epilib as just a library of functions and I could import into various python programs as required.
Is there a way to accomplish this?
That is not how python works, if you want to use numpy library in a module (in this case in eplib module), you need to import it in that module as well, eplib would get not the numpy module imported in your compare.py .
You should import numpy in eplib.py as -
import numpy as np
I do not think there would be any issue in efficiency, since once python imports a module for the first time, it caches the module in sys.modules , so whenever you re-import it (even if its in a different module) as long as its the same python process , Python would not re-import it, instead it would return the module object from sys.modules .
I am trying to write a function, which is itself loaded, to quickly import a bunch of modules globally.
I thought that, essentially, loaded modules could be treated as variables so I tried:
def loadMods():
global np
import numpy as np
and when I loaded numpy (calling np) there was no problem.
What I then did was to create a separate .py file called loadTest containing
# loadTest module
# coding: utf-8
def loadMod():
global np
import numpy as np
Then attempted to import numpy using this .py file in python (2.7):
import loadTest
loadTest.loadMod()
but now when attempting calling np I get
File "<stdin>", line 1, in <module>
NameError: name 'np' is not defined
Why does this occur? Any help or alternative ways of doing this would be much appreciated. Thanks a bunch :)
Instead of making a function to do this, why not make another module? You could name it something like modules.py and put all of your imports in there:
import numpy as np
import os
import sys
...
Then, all you need to do is a wildcard import:
from modules import *
and everything will be made available.
You must first define np like that.
In loadTest:
np=None
In somewhere other
import loadTest
loadTest.loadMod()
np=loadTest.np
I just installed ANACONDA and have set up my virtual environment and profile. When I enter a command like
from pandas import *
or
from numpy import random
the system pauses for a second before moving on to the next line, as expected. However, when I try to enter a command like
x = randn(100,100)
I get a message saying
name 'randn' is not defined
Also, when I run
imp.find_module("pandas")
I get
(None, 'C:\\Anaconda\\lib\\site-packages\\numpy', ('', '', 5))
Any ideas?
Your message title refers to scipy, but you didn't import anything from it, so I'm not sure why that's relevant. You did two imports:
from pandas import *
which I wouldn't actually recommend; I know it's done in some tutorials, but I prefer
import pandas as pd
to keep the namespace clean. In any case, randn isn't defined in the pandas namespace. Then you run
from numpy import random
which only adds one new name to the namespace: random. After you've done this, you can access randn via random.randn:
>>> from numpy import random
>>> random.randn(3)
array([-1.19504793, -0.54873061, -1.46225504])
If you really want to use simply randn, you could do
from numpy.random import randn