#### Overview of this book

Dancing with Python helps you learn Python and quantum computing in a practical way. It will help you explore how to work with numbers, strings, collections, iterators, and files. The book goes beyond functions and classes and teaches you to use Python and Qiskit to create gates and circuits for classical and quantum computing. Learn how quantum extends traditional techniques using the Grover Search Algorithm and the code that implements it. Dive into some advanced and widely used applications of Python and revisit strings with more sophisticated tools, such as regular expressions and basic natural language processing (NLP). The final chapters introduce you to data analysis, visualizations, and supervised and unsupervised machine learning. By the end of the book, you will be proficient in programming the latest and most powerful quantum computers, the Pythonic way.
Free Chapter
Chapter 1: Doing the Things That Coders Do
Part I: Getting to Know Python
Chapter 2: Working with Expressions
Chapter 3: Collecting Things Together
Chapter 4: Stringing You Along
Chapter 5: Computing and Calculating
Chapter 6: Defining and Using Functions
Chapter 7: Organizing Objects into Classes
Chapter 8: Working with Files
PART II: Algorithms and Circuits
Chapter 9: Understanding Gates and Circuits
Chapter 10: Optimizing and Testing Your Code
Chapter 11: Searching for the Quantum Improvement
PART III: Advanced Features and Libraries
Chapter 12: Searching and Changing Text
Chapter 13: Creating Plots and Charts
Chapter 14: Analyzing Data
Chapter 15: Learning, Briefly
References
Other Books You May Enjoy
Index
Appendices
Appendix B: Staying Current
Appendix C: The Complete UniPoly Class
Appendix D: The Complete Guitar Class Hierarchy
Appendix E: Notices
Appendix F: Production Notes

# 1.2 Expressions

An expression is a written combination of data with operations to perform on that data. That sounds quite formal, so imagine a mathematical formula like:

15 × 62 + 3 × 6 – 4 .

This expression contains six pieces of data: 15, 6, 2, 3, 6, and 4. There are five operations: multiplication, exponentiation, addition, multiplication, and subtraction. If I rewrite this using symbols often used in programming languages, it is:

15 * 6**2 + 3 * 6 - 4

See that repeated 6? Suppose I want to consider different numbers in its place. I can write the formula:

15 × x2 + 3 × x – 4

and the corresponding code expression:

15 * x**2 + 3 * x - 4

If I give x the value 6, I get the original expression. If I give it the value 11, I calculate:

15 * 11**2 + 3 * 11 - 4

We call x a variable and the process of giving it a value assignment. The expression

x = 11

means “assign the value 11 to x and wherever you see x, substitute in 11.” There is nothing special about x. I could have used y or something descriptive like kilograms.

An expression can contain multiple variables.

Exercise 1.3

In the expression

`a * x**2 + b * x + c` ,

what would you assign to a, b, c, and x to get

`7 * 3**2 + 2 * 3 + 1` ?

What assignments would you do for

`(-1)**2 + 9 * (-1) - 1` ?

The way we write data, operations, variables, names, and words together with the rules for combining them is called a programming language’s syntax. The syntax must be unambiguous and allow you to express your intentions elegantly. In this chapter, we do not focus on syntax but more on the ideas and the meaning, the semantics, of what programming languages can do. In Chapter 2, Working with Expressions, we begin to explore the syntax and features of Python.

We’re not limited to arithmetic in programming. Given two numbers x and y, if I saw maximum(x, y), I would expect it to return the larger value. Here “maximum” is the name of a function. We can write our own or use functions created, tested, optimized, and stored in libraries by others.