Nutils: a python based finite element package

Nutils is a MIT licensed package for Finite Elements applications.
Here you can find some examples how to use it
http://www.nutils.org/
Nutils by example

Reading lines till eof from standard input

If you want to read lines from the standard input until End-Of-File (eof), you can use the sys.stdin, for example:

#!/usr/bin/env python3
import sys

for line in sys.stdin:
    print(line,end="",flush=True)

Printing without newline

Print automatically adds a new line after printing its input variables and/or constants. To avoid this new line in Python2.6+ you can add a colon "," (without quotes) after the printing command, here is an example

print 'Hello',
print 'World'

In Python3, you can add the option end="". Example:

print('Hello',end="")
print('World')

Remember that from Python2.6+ you also can use the Python3 print command, adding

from __future__ import print_function

One Liner swaping of variables using tuples

In Python, it is possible to create a one liner code to swap the value of
two variables, this is how

a = 2
b = 4
print "a = ",a,"b = ",b

# One liner swap of variable using tuples

(a, b) = (b, a)
print "a = ",a,"b = ",b

# To improve the readability 
# you can write the tuple 
# without parenthesis, as
a, b = b, a

Matlab spy plot style in Python (sparse pattern)

The first time I used the command spy to show the sparse pattern of a sparse matrix, I wasn't satisfied with the result,

as a person who are used to Matlab plots. In this figure isn't easy to see the sparse pattern of the the matrix. After reading about the options available in the spy command, I found the option markersize. Changing the value of this parameter we can obtain a more familiar plot.

This is the code,

#!/usr/bin/env python
import scipy.sparse as sparse
import matplotlib.pyplot as plt
import scipy.io as io
import numpy as np

#Downloading the matrix from SPARSEKIT
problem = "SPARSKIT/drivcav/e05r0200"
mm = np.lib._datasource.Repository('ftp://math.nist.gov/pub/MatrixMarket2/')
f = mm.open('%s.mtx.gz' % problem)
A = io.mmread(f).tocsr()
f.close()
#Default Ploting
plt.spy(A)
plt.show()
#Closer to Matlab's result
plt.spy(A,markersize=1.0)
plt.show()

Example codes in github

You can find all the code published in this blog in github, please visit https://github.com/astudillor/codes_python_blog. Feel free to use and modify this code.

Checking the type of a variable or object

Recently, I came across to the problem of writing a function that behaves differently according the type of its single input parameter.  Due the fact that Python is a dynamically-typed language, this problem does not look  too easy to me at first glance. But fortunately, Python provides the build- in command  isinstance. This command receives two parameters, the first one is a object and the second is a class or tuple of classes. Then return  true is the object is an instance of the class or of the classes in the tuple. Let us exemplify the use of this function with a routine that print the type of its input parameter,

def printType(x):
    if isinstance(x,(int,long,float,complex)):
        print "It's a number"
        return
    if isinstance(x, str):
        print "It's a string"
        return
    if isinstance(x,list):
        print "It's a list"
        return
    if isinstance(x,dict):
        print "It's a dictionary"
        return
    if isinstance(x,tuple):
        print "It's a tuple"
        return