10_lambdas.md

10. Lambdas

Source: src/csharp_to_python_learning/concepts/03_functions_and_functional_tools/topic_10_lambdas.py

What C# developers usually expect C# developers usually expect explicit type declarations, predictable object lifetimes, and compile-time guidance.

C# example Simple equivalent:

var teams = new[] { "platform", "api", "ml" };
var ordered = teams.OrderBy(t => t.Length);
Console.WriteLine($"[{string.Join(", ", ordered)}]");

Advanced equivalent:

var records = new[]
{
    new { Name = "A", Score = 92 },
    new { Name = "B", Score = 81 },
};
var top = records.OrderByDescending(r => r.Score).ThenBy(r => r.Name).First();
Console.WriteLine($"{top.Name} {top.Score}");

Simple Python example from this file

teams = ["platform", "api", "ml"]
print(sorted(teams, key=lambda t: len(t)))

Advanced Python example from this file

records = [{"name": "A", "score": 92}, {"name": "B", "score": 81}]
top = max(records, key=lambda r: (r["score"], r["name"]))
print(top["name"], top["score"])

Python equivalent Python approaches this concept with less ceremony: Python lambdas are small expression-only functions, best used inline for short transformations. You still keep production discipline through tests, typing, and tooling.

Detailed explanation for C# developers Python lambdas are small expression-only functions, best used inline for short transformations. In practice, combine this with logging, tests, and type hints so the flexibility does not turn into ambiguity. Prefer small functions, clear data boundaries, and explicit contracts where behavior matters.

Common mistakes for C# developers

1. Assuming C# defaults apply directly in Lambdas without checking Python runtime behavior.
2. Skipping tests because dynamic code feels simpler at first; regressions grow quickly without guardrails.

Exercises

1. Rewrite one recent C# snippet in Python using this concept: Lambdas.
2. Add input validation, type hints, and one pytest test for the rewritten snippet.

Expected output

• ['ml', 'api', 'platform']
• A 92