cookbook.md

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Cookbook

Practical recipes:

Practical recipes for using the Pythonic C++ library.

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1. Parse CSV into list<dict> using var

Goal: Read a CSV file and store each row as a dictionary in a list, using the dynamic var type.

#include <pythonic/pythonic.hpp>
using namespace pythonic;

auto rows = list<dict<str, var>>{};
auto file = open("data.csv");
auto header = file.readline().strip().split(',');

for (auto line : file) {
	auto values = line.strip().split(',');
	dict<str, var> row;
	for (size_t i = 0; i < header.size(); ++i)
		row[header[i]] = values[i];
	rows.append(row);
}

Explanation:

• Reads the header to get column names.
• For each line, splits values and builds a dictionary.
• Appends each row dictionary to a list.

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2. Build and run a shortest-path example using graph

Goal: Create a graph, add edges, and compute shortest paths.

#include <pythonic/Graph.hpp>
using namespace pythonic;

graph g(5); // 5 nodes
g.add_edge(0, 1, 2);
g.add_edge(1, 2, 3);
g.add_edge(0, 3, 1);
g.add_edge(3, 4, 4);

auto dist = g.dijkstra(0);
print(dist); // Output: shortest distances from node 0

Explanation:

• Creates a graph with 5 nodes.
• Adds weighted edges.
• Runs Dijkstra’s algorithm from node 0.

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3. High-performance loop pattern using is_*() + as_*_unchecked()

Goal: Efficiently process a heterogeneous list by type-checking and fast casting.

#include <pythonic/pythonic.hpp>
using namespace pythonic;

list<var> items = {1, "hello", 3.14, 42};

for (const auto& x : items) {
	if (x.is_int()) {
		int val = x.as_int_unchecked(); // Fast, no type check
		print("int:", val);
	} else if (x.is_str()) {
		str s = x.as_str_unchecked();
		print("str:", s);
	}
}

Explanation:

• Use is_*() to check type.
• Use as_*_unchecked() for fast, unchecked access after confirming type.

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4. Combining comprehensions and functional helpers

Goal: Use list comprehensions and functional utilities for concise data processing.

#include <pythonic/pythonic.hpp>
using namespace pythonic;

list<int> nums = {1, 2, 3, 4, 5};
auto squares = [x * x for x : nums if x % 2 == 0]; // List comprehension

auto doubled = map([](int x) { return x * 2; }, nums); // Functional map

print(squares); // [4, 16]
print(list<int>(doubled)); // [2, 4, 6, 8, 10]

Explanation:

• List comprehensions for filtering and transforming.
• Functional helpers like map for concise operations.

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