python related (numpy and scipy) - python-2.7

Question

when i run command import numpy as np or import scipy as sp, it gives me error like:
Traceback (most recent call last):
File "<pyshell#2>", line 1, in <module>
import numpy as np
ImportError: No module named numpy
Traceback (most recent call last):
File "<pyshell#8>", line 1, in <module>
import scipy as sp
ImportError: No module named scipy

Answer 1

(Disclaimer: there are already tons of well established way / tutorials on the internet. I'm merely posting this to hopefully help out quickly)
 What you want to achieve
To install a library (e.g. numpy, scipy) locally on a machine (e.g. laptop, server, etc.) and import that library from a Python code.
 One of the solutions: Anaconda
One of the popular / quick ways in the Python scientific community is to do this via Anaconda (disclaimer 2: I personally prefer Anaconda due to its ease of enabling me to switch / play with different Python environments). Here is the step by step instructions:
Download and install the Anaconda distribution onto the machine locally.
Create a file environment.yml and store it anywhere you like (e.g. a subdirectory within your home directory). The file looks like this gist file - tweak it to your taste (e.g. choose Python version 2.x vs 3.x, add/remove/edit dependencies, etc.)
Within the same directory where you've created the environment.yml, create a conda environment by: conda env create -f environment.yml. For this particular gist file, it will create a conda environment (called "helloworld") with the specific Python version (2.7) and the anaconda package (which includes the popular numpy and scipy libraries).
Activate the environment (i.e. "go inside that environment") by: source activate helloworld (replace "helloworld" with whatever name you specified in environment.yml).
Now you are in the "helloworld" conda environment, start up a python console: jupyter console.
Now try importing stuff within this console:
Python 2.7.13 |Anaconda 4.4.0 (x86_64)| (default, Dec 20 2016, 23:05:08)
Type "copyright", "credits" or "license" for more information.
IPython 5.3.0 -- An enhanced Interactive Python.
? -> Introduction and overview of IPython's features.
%quickref -> Quick reference.
help -> Python's own help system.
object? -> Details about 'object', use 'object??' for extra details.
In [1]: import numpy as np
In [2]: import scipy as sp
In [3]: np.version.version
Out[3]: '1.12.1'
In [4]: sp.version.version
Out[4]: '0.19.0'
(to quit console just do a Ctrl + D to go back to command line)
For step 5 above, also try out:
jupyter notebook
jupyter qtconsole
And play with the python commands.
When you are done with the conda environment, just "deactivate" (i.e. get out of) it by doing this in the command line: source deactivate.
Top tip: don't forget step 4 - this defines which conda environment you are in (i.e. which python version and libraries available etc.). I occasionally ommited step 4 by accident and get that error "no module named numpy", etc.)
See this Anaconda get started guide for more info.
The non Anaconda way
If you would like to avoid Anaconda all together, just simply do this in the command line:
Install the numpy and scipy libraries:
pip install numpy
pip install scipy
Start a Python interpreter:
python
Do the library import stuff within the Python interpreter:
>>> import numpy as np
>>> import scipy as sp
>>> np.version.version
'1.11.3'
>>> sp.version.version
'1.11.3'
 Additional alternatives
You could try out the Python VirtualEnv - though I've never really used it since I've started using Anaconda.