Computer Program: a definition

• Is a translation of an algorithm into a programming language.
• Has a valid syntax and semantics.
• Is a set of instructions that a computer follows to perform a task.

Programming language

A programming language is a system of notation for writing computer programs. It is described in terms of syntax and semantics. (Wikipedia)

Python

• A high-level interpreted language.
• Easy to learn and use.
• Very popular and widely used for AI data science.
• Main language for this semester.

Java

• A high-level compiled language.
• class-based and object-oriented: more complex to learn
• Very present in the industry.
• Shown as an example this semester, studied in the next one.

Choosing the relevant language depends on various factors:

Adaptadness, performance, ease of use, community, etc.

Main steps:

1. Writing: the programmer writes the code.
2. Lexing: the code is transformed into tokens.
3. Parsing: the tokens are transformed into an abstract syntax tree.
4. Compilation: the abstract syntax tree is transformed into machine code.
5. Execution: the machine code is executed by the computer.

Many very simple rules make reading source code easier:

• Indentation: to show the structure of the code.
• Naming conventions: to make the code self-explanatory.
• Avoid constants: use variables instead.
• Avoid global variables: use local variables instead.

• Comments: to explain the logic of the code, not the syntax.
• Documentation: to explain the purpose of the code.
• Modularity: to split the code into small, reusable parts.

• Structured programming: to avoid spaghetti code.
• Testing: to ensure the code works as expected.
• Built-in functions and librairies: to avoid reinventing the wheel.

• PEP 8: Python Enhancement Proposals 8, a style guide for Python code.
• Pylint: a tool to check if a module satisfies a coding standard.
• Comments and documents your code.
• Type hints: to specify the type of variables.
• mypy: a static type checker

Coding norms may vary from one language to another.

The code does not respect the syntax of the language.

# The string to manipulate
s = "IMT Atlantique"

# Loop to append to a new string
result = ""
for i j in range(len(s)):
    result = s[i] + result

SyntaxError: invalid syntax

The code is syntactically correct but produces an error during execution.

# Ask user at runtime for a value
den = input("Please enter the value of the denominator")

# Perform a computation
result = 42 / den
print(result)

When using random values, the program may not always produce the same result. Thus, it may be difficult to debug.

However, it is possible to set a seed to ensure reproducibility.

# Needed imports
import random

# Set the seed
random.seed(42)