Python has many different types and variables are dynamic and can change types (like MATLAB). Some of the most commonly used in-built types are:
* integer and floating point scalars
* strings
* tuples
* lists
* dictionary
N-dimensional arrays and other types are supported through common modules (e.g., numpy, scipy, scikit-learn).
```
a = 4
b = 3.6
c = 'abc'
d = [10,20,30]
e = {'a' : 10, 'b': 20}
```
Any variable can be printed using the function:
```
print(...)
```
> Python 3 versus python 2:
> Print - for the print statement the brackets are compulsory for *python 3*, but are optional in python 2. So you will see plenty of code without the brackets but you should get into the habit of using them.
> Division - in python 3 all division is floating point (like in MATLAB), even if the values are integers, but in python 2 integer division works like it does in C.
## Strings
Strings can be specified using single quotes *or* double quotes - as long as they are matched.
Strings can be dereferenced like lists (see later).
For example:
```
s1="test string"
s2='another test string'
```
You can also use triple quotes to capture multi-line strings. For example:
```
s3='''This is
a string over
multiple lines
'''
print(s3)
This is
a string over
multiple lines
```
## Tuples and Lists
Anything can be stored within a list and consistency is not required. For example:
```
a=[1,'mj',-5.4]
```
### Dereferencing
Square brackets are used to dereference lists, dictionaries, etc. For example:
```
d = [10,20,30]
d[1]
20
```
---- use of -1 as an index value
> Pitfall:
> Python uses zero-based indexing, unlike MATLAB
> * a=[10,20,30,40,50,60]
> * a[0]
> 10
> * a[2]
> 30
### List operations
Addition and multiplication can be used with lists, where multiplication implements replication.
```
d=[10,20,30]
d*2
[10, 20, 30, 10, 20, 30]
```
There are also other operations such as:
```
d.append(40)
```
USE DIR() TO GET MORE INFO FOR ANY PARTICULAR OBJECT - OR GOOGLE!
## Dictionaries
## Combinations
Can nest these arbitrarily without needing consistency. For example:
```
a=[ [3,5,7] , ['a','e','i','o','u'] , { } ]
```
## Copying and references
** demonstrate difference between mutable and immutable types
a = 7
b = a
a = 2348
print(b)
a = [7]
b = a
a[0] = 8888
print(b)
> Pitfall:
> Slicing syntax is also different from MATLAB (second number is one plus final index)
> * a=[10,20,30,40,50,60]
> * a[0:3] # same as a(1:3) in MATLAB
> [10, 20, 30]
> * a[1:3] # same as a(2:3) in MATLAB
> [20, 30]
> Pitfall:
> Cannot use a list as indices instead of an integer or a slice
> * b=[3,4]
> * a[b]
> TypeError: list indices must be integers or slices, not list
