Further information
Contents
Further information#
Are there other ways to access elements in tuples?#
You have seen in this chapter how to access a single element in a tuple. There are various ways of indexing tuples:
Why does range
, itertools.permutations
and itertools.combinations
not directly give the elements?#
When you run either of the three range
, itertools.permutations
or
itertools.combinations
tools this is an example of creating a
generator. This allows the creation of the instructions to build
something without building it.
In practice this means that you can create large sets without needing to generate them until required.
How does the summation notation \(\sum\) correspond to the code?#
The sum
command corresponds to the mathematical \(\sum\) notation. Here
are a few examples showing the sum
command, the \(\sum\) notation but
also the prose describing:
Mathematics |
Python |
Prose |
---|---|---|
\[\sum_{i=1}^{100}i ^2\]
|
sum(i ** 2 for i in range(1, 101))
|
The sum of the square of the integers from 1 to 100 (inclusive). |
\[\begin{split}\sum_{\begin{array}{c}i=1\\\text{if }i\text{ is prime}\end{array}}^{100}i ^2\end{split}\]
|
sum(i ** 2 for i in range(1, 101) if sym.isprime(i))
|
The sum of the square of the integers from 1 to 100 (inclusive) if they are prime. |
\[\begin{split}\sum_{\begin{array}{c}i\in{S}\\\text{if }i\text{ is prime}\end{array}}i ^2\end{split}\]
|
sum(i ** 2 for i in S if sym.isprime(i))
|
The sum of the square of the elements in the collection \(S\) if they are prime. |