The Kitchin Research Group

A list in python is data separated by commas in square brackets. Here, we might store the following data in a variable to describe the Antoine coefficients for benzene and the range they are relevant for [Tmin Tmax]. Lists are flexible, you can put anything in them, including other lists. We access the elements of the list by indexing:

c = ['benzene', 6.9056, 1211.0, 220.79, [-16, 104]]
print c[0]
print c[-1]

a,b = c[0:2]
print a,b

name, A, B, C, Trange = c
print Trange

benzene
[-16, 104]
benzene 6.9056
[-16, 104]

Lists are “mutable”, which means you can change their values.

a = [3, 4, 5, [7, 8], 'cat']
print a[0], a[-1]
a[-1] = 'dog'
print a

3 cat
>>> [3, 4, 5, [7, 8], 'dog']

Tuples are immutable; you cannot change their values. This is handy in cases where it is an error to change the value. A tuple is like a list but it is enclosed in parentheses.

a = (3, 4, 5, [7, 8], 'cat')
print a[0], a[-1]
a[-1] = 'dog'

3 cat
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'tuple' object does not support item assignment

Python does not exactly have the same thing as a struct in Matlab. You can achieve something like it by defining an empty class and then defining attributes of the class. You can check if an object has a particular attribute using hasattr.

class Antoine:
    pass

a = Antoine()
a.name = 'benzene'
a.Trange = [-16, 104]

print a.name
print hasattr(a, 'Trange')
print hasattr(a, 'A')

benzene
True
False

The analog of the containers.Map in Matlab is the dictionary in python. Dictionaries are enclosed in curly brackets, and are composed of key:value pairs.

s = {'name':'benzene',
     'A':6.9056,
     'B':1211.0}

s['C'] = 220.79
s['Trange'] = [-16, 104]

print s
print s['Trange']

{'A': 6.9056, 'C': 220.79, 'B': 1211.0, 'name': 'benzene', 'Trange': [-16, 104]}
[-16, 104]

s = {'name':'benzene',
     'A':6.9056,
     'B':1211.0}

print 'C' in s
# default value for keys not in the dictionary
print s.get('C', None)

print s.keys()
print s.values()

False
None
['A', 'B', 'name']
[6.9056, 1211.0, 'benzene']

We have examined four data structures in python. Note that none of these types are arrays/vectors with defined mathematical operations. For those, you need to consider numpy.array.