18a

2020/sketch_2020_08_18a/arcs.py

@@ -0,0 +1,171 @@
+# -*- coding: utf-8 -*-
+
+ROTATION = {0: 0,
+            BOTTOM: 0,
+            DOWN: 0,
+            1: HALF_PI,
+            LEFT: HALF_PI,
+            2: PI,
+            TOP: PI,
+            UP: PI,
+            3: PI + HALF_PI,
+            RIGHT: PI + HALF_PI,
+            BOTTOM + RIGHT: 0,
+            DOWN + RIGHT: 0,
+            DOWN + LEFT: HALF_PI,
+            BOTTOM + LEFT: HALF_PI,
+            TOP + LEFT: PI,
+            UP + LEFT: PI,
+            TOP + RIGHT: PI + HALF_PI,
+            UP + RIGHT: PI + HALF_PI,
+            }
+
+def quarter_circle(x, y, radius, quadrant):
+    circle_arc(x, y, radius, ROTATION[quadrant], HALF_PI)
+
+def half_circle(x, y, radius, quadrant):
+    circle_arc(x, y, radius, ROTATION[quadrant], PI)
+
+def circle_arc(x, y, radius, start_ang, sweep_ang):
+    arc(x, y, radius * 2, radius * 2, start_ang, start_ang + sweep_ang)
+
+def poly_arc(x, y, radius, start_ang, sweep_ang, num_points=2):
+    angle = sweep_ang / int(num_points)
+    a = start_ang
+    with beginShape():
+        while a <= start_ang + sweep_ang:
+            sx = x + cos(a) * radius
+            sy = y + sin(a) * radius
+            vertex(sx, sy)
+            a += angle
+
+def arc_poly(x, y, d, _, start_ang, end_ang, num_points=5):
+    sweep_ang = end_ang - start_ang
+    angle = sweep_ang / int(num_points)
+    a = start_ang
+    with beginShape():
+        while a <= end_ang:
+            sx = x + cos(a) * d / 2
+            sy = y + sin(a) * d / 2
+            vertex(sx, sy)
+            a += angle
+
+def bar(x1, y1, x2, y2, thickness=None, shorter=0, ends=(1, 1)):
+    """
+    O código para fazer as barras, dois pares (x, y),
+    um parâmetro de encurtamento: shorter
+    """
+    L = dist(x1, y1, x2, y2)
+    if not thickness:
+        thickness = 10
+    with pushMatrix():
+        translate(x1, y1)
+        angle = atan2(x1 - x2, y2 - y1)
+        rotate(angle)
+        offset = shorter / 2
+        line(thickness / 2, offset, thickness / 2, L - offset)
+        line(-thickness / 2, offset, -thickness / 2, L - offset)
+        if ends[0]:
+            half_circle(0, offset, thickness / 2, UP)
+        if ends[1]:
+            half_circle(0, L - offset, thickness / 2, DOWN)
+
+def var_bar(p1x, p1y, p2x, p2y, r1, r2=None):
+    """
+    Tangent/tangent shape on 2 circles of arbitrary radius
+    """
+    if r2 is None:
+        r2 = r1
+    #line(p1x, p1y, p2x, p2y)
+    d = dist(p1x, p1y, p2x, p2y)
+    ri = r1 - r2
+    if d > abs(ri):
+        rid = (r1 - r2) / d
+        if rid > 1:
+            rid = 1
+        if rid < -1:
+            rid = -1
+        beta = asin(rid) + HALF_PI
+        with pushMatrix():
+            translate(p1x, p1y)
+            angle = atan2(p1x - p2x, p2y - p1y)
+            rotate(angle + HALF_PI)
+            x1 = cos(beta) * r1
+            y1 = sin(beta) * r1
+            x2 = cos(beta) * r2
+            y2 = sin(beta) * r2
+            #print((d, beta, ri, x1, y1, x2, y2))
+            beginShape()  
+            b_arc(0, 0, r1 * 2, r1 * 2,
+                -beta - PI, beta - PI, mode=2)
+            b_arc(d, 0, r2 * 2, r2 * 2,
+                beta - PI, PI - beta, mode=2)
+            endShape(CLOSE)
+    else:
+        ellipse(p1x, p1y, r1 * 2, r1 * 2)
+        ellipse(p2x, p2y, r2 * 2, r2 * 2)
+        
+def b_arc(cx, cy, w, h, start_angle, end_angle, mode=0):
+    """
+    A bezier approximation of an arc
+    using the same signature as the original Processing arc()
+    mode: 0 "normal" arc, using beginShape() and endShape()
+              1 "middle" used in recursive call of smaller arcs
+              2 "naked" like normal, but without beginShape() and endShape()
+                 for use inside a larger PShape
+    """
+    theta = end_angle - start_angle
+    # Compute raw Bezier coordinates.
+    if mode != 1 or abs(theta) < HALF_PI:
+        x0 = cos(theta / 2.0)
+        y0 = sin(theta / 2.0)
+        x3 = x0
+        y3 = 0 - y0
+        x1 = (4.0 - x0) / 3.0
+        if y0 != 0:
+            y1 = ((1.0 - x0) * (3.0 - x0)) / (3.0 * y0)  # y0 != 0...
+        else:
+            y1 = 0
+        x2 = x1
+        y2 = 0 - y1
+        # Compute rotationally-offset Bezier coordinates, using:
+        # x' = cos(angle) * x - sin(angle) * y
+        # y' = sin(angle) * x + cos(angle) * y
+        bezAng = start_angle + theta / 2.0
+        cBezAng = cos(bezAng)
+        sBezAng = sin(bezAng)
+        rx0 = cBezAng * x0 - sBezAng * y0
+        ry0 = sBezAng * x0 + cBezAng * y0
+        rx1 = cBezAng * x1 - sBezAng * y1
+        ry1 = sBezAng * x1 + cBezAng * y1
+        rx2 = cBezAng * x2 - sBezAng * y2
+        ry2 = sBezAng * x2 + cBezAng * y2
+        rx3 = cBezAng * x3 - sBezAng * y3
+        ry3 = sBezAng * x3 + cBezAng * y3
+        # Compute scaled and translated Bezier coordinates.
+        rx, ry = w / 2.0, h / 2.0
+        px0 = cx + rx * rx0
+        py0 = cy + ry * ry0
+        px1 = cx + rx * rx1
+        py1 = cy + ry * ry1
+        px2 = cx + rx * rx2
+        py2 = cy + ry * ry2
+        px3 = cx + rx * rx3
+        py3 = cy + ry * ry3
+        # Debug points... comment this out!
+        # stroke(0)
+        # ellipse(px3, py3, 15, 15)
+        # ellipse(px0, py0, 5, 5)
+    # Drawing
+    if mode == 0:  # 'normal' arc (not 'middle' nor 'naked')
+        beginShape()
+    if mode != 1:  # if not 'middle'
+        vertex(px3, py3)
+    if abs(theta) < HALF_PI:
+        bezierVertex(px2, py2, px1, py1, px0, py0)
+    else:
+        # to avoid distortion, break into 2 smaller arcs
+        b_arc(cx, cy, w, h, start_angle, end_angle - theta / 2.0, mode=1)
+        b_arc(cx, cy, w, h, start_angle + theta / 2.0, end_angle, mode=1)
+    if mode == 0:  # end of a 'normal' arc
+        endShape()

2020/sketch_2020_08_18a/graph.py

@@ -0,0 +1,338 @@
+#*- coding: utf-8 -*-
+
+"""
+A simple Python graph class, demonstrating the essential facts and functionalities of graphs
+based on https://www.python-course.eu/graphs_python.php and https://www.python.org/doc/essays/graphs/
+"""
+
+from random import choice
+
+class Graph(object):
+
+    def __init__(self, graph_dict=None):
+        """
+        Initialize a graph object with dictionary provided,
+        if none provided, create an empty one.
+        """
+        if graph_dict is None:
+            graph_dict = {}
+        self.__graph_dict = graph_dict
+
+    def __len__(self):
+        return len(self.__graph_dict)
+
+    def vertices(self):
+        """Return the vertices of graph."""
+        return list(self.__graph_dict.keys())
+
+    def edges(self):
+        """Return the edges of graph """
+        return self.__generate_edges()
+
+    def add_vertex(self, vertex):
+        """
+        If the vertex "vertex" is not in self.__graph_dict,
+        add key "vertex" with an empty list as a value,
+        otherwise, do nothing.
+        """
+        if vertex not in self.__graph_dict:
+            self.__graph_dict[vertex] = []
+
+    def add_edge(self, edge):
+        """
+        Assuming that edge is of type set, tuple or list;
+        add edge between vertices. Can add multiple edges!
+        """
+        edge = set(edge)
+        vertex1 = edge.pop()
+        if edge:
+            # not a loop
+            vertex2 = edge.pop()
+            if vertex1 in self.__graph_dict:
+                self.__graph_dict[vertex1].append(vertex2)
+            else:
+                self.__graph_dict[vertex1] = [vertex2]
+            if vertex2 in self.__graph_dict:
+                self.__graph_dict[vertex2].append(vertex1)
+            else:
+                self.__graph_dict[vertex2] = [vertex1]
+        else:
+            # a loop
+            if vertex1 in self.__graph_dict:
+                self.__graph_dict[vertex1].append(vertex1)
+            else:
+                self.__graph_dict[vertex1] = [vertex1]
+
+    def remove_vertex(self, vert):
+        del self.__graph_dict[vert]
+        for k in self.__graph_dict.keys():
+            if vert in self.__graph_dict[k]:
+                self.__graph_dict[k].remove(vert)
+
+    def remove_edge(self, edge):
+        edge = set(edge)
+        vertex1 = edge.pop()
+        if edge:
+            vertex2 = edge.pop()
+            self.__graph_dict[vertex1].remove(vertex2)
+            self.__graph_dict[vertex2].remove(vertex1)
+        else:
+            self.__graph_dict[vertex1].remove(vertex1)
+
+    def __generate_edges(self):
+        """
+        Generate the edges, represented as sets with one
+        (a loop back to the vertex) or two vertices.
+        """
+        edges = []
+        for vertex in self.__graph_dict:
+            for neighbour in self.__graph_dict[vertex]:
+                if {neighbour, vertex} not in edges:
+                    edges.append({vertex, neighbour})
+        return edges
+
+    def __str__(self):
+        res = "vertices: "
+        for k in self.__graph_dict:
+            res += str(k) + " "
+        res += "\nedges: "
+        for edge in self.__generate_edges():
+            res += str(edge) + " "
+        return res
+
+    def find_isolated_vertices(self):
+        """
+        Return a list of isolated vertices.
+        """
+        graph = self.__graph_dict
+        isolated = []
+        for vertex in graph:
+            print(isolated, vertex)
+            if not graph[vertex]:
+                isolated += [vertex]
+        return isolated
+
+    def find_path(self, start_vertex, end_vertex, path=[]):
+        """
+        Find a path from start_vertex to end_vertex in graph.
+        """
+        graph = self.__graph_dict
+        path = path + [start_vertex]
+        if start_vertex == end_vertex:
+            return path
+        if start_vertex not in graph:
+            return None
+        for vertex in graph[start_vertex]:
+            if vertex not in path:
+                extended_path = self.find_path(vertex,
+                                               end_vertex,
+                                               path)
+                if extended_path:
+                    return extended_path
+        return None
+
+    def find_all_paths(self, start_vertex, end_vertex, path=[]):
+        """
+        Find all paths from start_vertex to end_vertex.
+        """
+        graph = self.__graph_dict
+        path = path + [start_vertex]
+        if start_vertex == end_vertex:
+            return [path]
+        if start_vertex not in graph:
+            return []
+        paths = []
+        for vertex in graph[start_vertex]:
+            if vertex not in path:
+                extended_paths = self.find_all_paths(vertex,
+                                                     end_vertex,
+                                                     path)
+                for p in extended_paths:
+                    paths.append(p)
+        return paths
+
+    def is_connected(self,
+                     vertices_encountered=None,
+                     start_vertex=None):
+        """Find if the graph is connected."""
+        if vertices_encountered is None:
+            vertices_encountered = set()
+        gdict = self.__graph_dict
+        vertices = list(gdict.keys())  # "list" necessary in Python 3
+        if not start_vertex:
+            # chosse a vertex from graph as a starting point
+            start_vertex = vertices[0]
+        vertices_encountered.add(start_vertex)
+        if len(vertices_encountered) != len(vertices):
+            for vertex in gdict[start_vertex]:
+                if vertex not in vertices_encountered:
+                    if self.is_connected(vertices_encountered, vertex):
+                        return True
+        else:
+            return True
+        return False
+
+    def vertex_degree(self, vertex):
+        """
+        Return the number of edges connecting to a vertex (the number of adjacent vertices).
+        Loops are counted double, i.e. every occurence of vertex in the list of adjacent vertices.
+        """
+        adj_vertices = self.__graph_dict[vertex]
+        degree = len(adj_vertices) + adj_vertices.count(vertex)
+        return degree
+
+    def degree_sequence(self):
+        """Calculates the degree sequence."""
+        seq = []
+        for vertex in self.__graph_dict:
+            seq.append(self.vertex_degree(vertex))
+        seq.sort(reverse=True)
+        return tuple(seq)
+
+    @staticmethod
+    def is_degree_sequence(sequence):
+        """
+        Return True, if the sequence is a degree sequence (non-increasing),
+        otherwise return False.
+        """
+        return all(x >= y for x, y in zip(sequence, sequence[1:]))
+
+    def delta(self):
+        """Find minimum degree of vertices."""
+        min = 100000000
+        for vertex in self.__graph_dict:
+            vertex_degree = self.vertex_degree(vertex)
+            if vertex_degree < min:
+                min = vertex_degree
+        return min
+
+    def Delta(self):
+        """Finde maximum degree of vertices."""
+        max = 0
+        for vertex in self.__graph_dict:
+            vertex_degree = self.vertex_degree(vertex)
+            if vertex_degree > max:
+                max = vertex_degree
+        return max
+
+    def density(self):
+        """Calculate the graph density."""
+        g = self.__graph_dict
+        V = len(g.keys())
+        E = len(self.edges())
+        return 2.0 * E / (V * (V - 1))
+
+    def diameter(self):
+        """Calculates the graph diameter."""
+
+        v = self.vertices()
+        pairs = [
+            (v[i],
+             v[j]) for i in range(
+                len(v)) for j in range(
+                i + 1,
+                len(v) - 1)]
+        smallest_paths = []
+        for (s, e) in pairs:
+            paths = self.find_all_paths(s, e)
+            smallest = sorted(paths, key=len)[0]
+            smallest_paths.append(smallest)
+
+        smallest_paths.sort(key=len)
+
+        # longest path is at the end of list,
+        # i.e. diameter corresponds to the length of this path
+        diameter = len(smallest_paths[-1]) - 1
+        return diameter
+
+    @staticmethod
+    def erdoes_gallai(dsequence):
+        """
+        Check if Erdoes-Gallai inequality condition is fullfilled.
+        """
+        if sum(dsequence) % 2:
+            # sum of sequence is odd
+            return False
+        if Graph.is_degree_sequence(dsequence):
+            for k in range(1, len(dsequence) + 1):
+                left = sum(dsequence[:k])
+                right = k * (k - 1) + sum([min(x, k) for x in dsequence[k:]])
+                if left > right:
+                    return False
+        else:
+            # sequence is increasing
+            return False
+        return True
+
+    # Code by Eryk Kopczyński
+    def find_shortest_path(self, start, end):
+        from collections import deque
+        graph = self.__graph_dict
+        dist = {start: [start]}
+        q = deque((start,))
+        while len(q):
+            at = q.popleft()
+            for next in graph[at]:
+                if next not in dist:
+                    # dist[next] = [dist[at], next]
+                    # less efficient but nicer output
+                    dist[next] = dist[at] + [next]
+                    q.append(next)
+        return dist.get(end)
+
+    ##############
+    def is_cyclic(self):
+        """
+        Returns true if the graph contains a cycle, else false.
+        """
+        # Mark all the vertices as not visited
+        visited = [False] * len(self)
+        # Call helper function to detect cycle in different DFS trees
+        for i, v in enumerate(visited):
+            # Don't recur for u if it is already visited
+            if v == False:
+                if self.dfs(i, visited, -1):
+                    return True
+        return False
+
+    def dfs(self, v, visited, parent):
+        # Mark the current node as visited
+        visited[v] = True
+        # Recur for all the vertices adjacent to this vertex
+        for i in self.__graph_dict[v]:
+            # If the node is not visited then recurse on it
+            if visited[i] == False:
+                if(self.dfs(i, visited, v)):
+                    return True
+            # If an adjacent vertex is visited and not parent of current
+            # vertex, then there is a cycle
+            elif parent != i:
+                return True
+        return False
+
+    ##############
+
+    def get_random_vertex(self):
+        return choice(self.vertices())
+
+    @staticmethod
+    def random_graph(names,
+                     connect_rate=.9,
+                     allow_loops=True,
+                     allow_cyclic=False,
+                     connected=False):
+        vertices = set(names)
+        while True:
+            graph = Graph()
+            for v in vertices:
+                graph.add_vertex(v)
+                if random(1) < connect_rate:
+                    if allow_loops:
+                        names = list(vertices)
+                    else:
+                        names = list(vertices - set((v,)))
+                    graph.add_edge({v, choice(names)})
+            if not connected or graph.is_connected():
+                if allow_cyclic or not graph.is_cyclic():
+                    break
+        return graph

2020/sketch_2020_08_18a/grid.py

@@ -0,0 +1,115 @@
+#*- coding: utf-8 -*-
+
+from __future__ import division, print_function
+from random import sample, choice
+
+
+class Grid():
+
+    def __init__(self, graph, width, height, margin=None, mode=0):
+        """
+        mode 0: heavy center
+        mode 1: heavy perifery
+        """
+        margin = margin or width / 40
+        cols, rows = dim_grid(len(graph))
+        w, h = (width - margin * 2) / cols, (height - margin * 2) / rows
+        points = []
+        for i in range(cols * rows):
+            c = i % cols
+            r = i // rows
+            x = margin + w * 0.5 + c * w  # - 14 * (r % 2) + 7
+            y = margin + h * 0.5 + r * h  # - 14 * (c % 2) + 7
+            z = 0
+            points.append([x, y, z])
+        points = sorted(
+            points, key=lambda p: dist(p[0], p[1], width / 2, height / 2))
+        if mode == 0:
+            v_list = reversed(
+                sorted(graph.vertices(), key=graph.vertex_degree))
+        elif mode == 1:
+            v_list = sorted(graph.vertices(), key=graph.vertex_degree)
+        else:
+            v_list = graph.vertices()
+            print("random mode")
+        
+        Grid.w, Grid.h = w, h
+        self.graph = graph
+        self.grid = {v: p for v, p in zip(v_list, points)}
+        recalculate_sizes_from_v_deg(self.graph, self)
+
+    def __getitem__(self, k):
+        return self.grid[k]
+
+    def __setitem__(self, k, v):
+        self.grid[k] = v
+
+    def __len__(self):
+        return len(self.grid)
+    
+    def keys(self):
+        return self.grid.keys()
+
+    def values(self):
+        return self.grid.values()
+
+    def __iter__(self):
+        return iter(self.grid)
+
+    def swap(self, num=2):
+        grid = self.grid
+        graph = self.graph
+        fail = 0
+        n = m = edge_distances(graph, grid)
+        while m <= n and fail < len(graph) ** 2:
+            new_grid = dict(grid)
+            if num == 2:
+                a, b = sample(graph.vertices(), 2)
+                new_grid[a], new_grid[b] = new_grid[b], new_grid[a]
+            else:
+                ks = sample(graph.vertices(), num)
+                vs = [grid[k] for k in sample(ks, num)]
+                for k, v in zip(ks, vs):
+                    new_grid[k] = v
+            n = edge_distances(graph, new_grid)
+            if m > n:
+                t = "{:.2%} at: {} tries of {}v shuffle/swap" \
+                    .format((n - m) / m, fail + 1, num)
+                print("\n" + t, end="")
+                recalculate_sizes_from_v_deg(graph, new_grid)
+                self.grid = new_grid
+            else:
+                fail += 1
+        print(".", end='')
+    
+    
+
+def dim_grid(n):
+    a = int(sqrt(n))
+    b = n // a
+    if a * b < n:
+        b += 1
+    print(u'{}: {} × {} ({})'.format(n, a, b, a * b))
+    return a, b
+
+def edge_distances(graph, grid):
+    total = 0
+    for edge in graph.edges():
+        if len(edge) == 2:
+            a, b = edge
+            d = PVector.dist(PVector(*grid[a]),
+                             PVector(*grid[b]))
+            total += d
+    return total
+
+
+def recalculate_sizes_from_v_deg(graph, grid):
+    u = Grid.w / 10
+    for k in grid.keys():
+        grid[k][2] = u * graph.vertex_degree(k)
+    return u
+
+def v_dist(a, b):
+    xa, ya, _ = a
+    xb, yb, _ = b
+    return dist(xa, ya, xb, yb)

2020/sketch_2020_08_18a/sketch_2020_08_18a.pyde

@@ -0,0 +1,134 @@
+from __future__ import print_function, division
+from random import choice
+from graph import Graph
+from grid import *  # setup_grid, grid_swap, edge_distances
+from arcs import var_bar
+
+thread_running = False
+gx, gy = 0, 100
+viz_stat = False
+selected_v = None
+
+def setup():
+    size(500, 500)
+    colorMode(HSB)
+    textAlign(CENTER, CENTER)
+    f = createFont("Source Code Pro Bold", 12)
+    textFont(f)
+    setup_graph()
+
+def setup_graph(mode=0):
+    # create a random graph and a dict of grid postions for its vertices
+    global graph, grid, m, d
+    graph = Graph.random_graph(range(64),
+                               connect_rate=.95,
+                               allow_loops=False,
+                               connected=True,
+                               allow_cyclic=False)
+    grid = Grid(graph,
+                width=width,
+                height=width,
+                margin=10,
+                mode=mode)
+    d = recalculate_sizes_from_v_deg(graph, grid)
+    m = edge_distances(graph, grid)  # "metric", sum of edge distances
+    print("Cyclic: " + str(graph.is_cyclic()))
+
+def draw():
+    background(200)
+    for e in graph.edges():
+        va = e.pop()
+        xa, ya, za = grid[va]
+        if len(e) == 1:
+            vb = e.pop()
+            xb, yb, zb = grid[vb]
+            fill(240)
+            degree = ((za + zb) / 2) / d
+            strokeWeight(map(degree, 1.5, 5, 5, 1))
+            var_bar(xa, ya, xb, yb, za, zb)
+
+    for v in grid.keys():
+        x, y, z = grid[v]
+        if v == selected_v:
+            fill(0)
+        elif mouse_near(v):
+            fill(128)
+        else:
+            noFill()
+        strokeWeight(1)
+        circle(x, y, 10)
+        if viz_stat:
+            fill(255)
+            text("{}:{}".format(v, graph.vertex_degree(v)).upper(),
+                 x - 15, y - 5)
+    fill(100)
+    text(int(m / 200), 20, 20)
+
+    if selected_v:
+        x, y, _ = grid[selected_v]
+        stroke(0)
+        strokeWeight(5)
+        line(x, y, mouseX, mouseY)
+
+
+def keyTyped():
+    global gx, gy, viz_stat
+    if key == 'r':
+        setup_graph(mode=0)
+        gx, gy = 0, 100
+    if key == 'e':
+        setup_graph(mode=1)
+        gx, gy = 0, 100
+    if key == 'R':
+        setup_graph(mode=2)
+        gx, gy = 0, 100
+    elif key == 'v':
+        viz_stat = not viz_stat
+    else:
+        if not thread_running:
+            thread("swapping")
+
+def swapping():
+    global grid, thread_running, gx, gy, m
+    if str(key) not in 'sc23456789':
+        return
+    thread_running = True
+    m = edge_distances(graph, grid)
+    len_graph = len(graph)
+    multiple = 1 if mousePressed else 100
+    for _ in range(multiple):
+        if key == 's':
+            grid.swap(num=len_graph)
+        if key in '234556789':
+            grid.swap(num=int(key))
+        n = edge_distances(graph, grid)
+        gx += 1
+        if n < m:
+            gy -= gy * (m - n) / m
+            m = n
+    thread_running = False
+
+def mouse_near(v):
+    x, y, _ = grid[v]
+    return dist(x, y, mouseX, mouseY) < 12
+
+def mousePressed():
+    global selected_v
+    for v in grid.keys():
+        if mouse_near(v):
+            selected_v = v
+            return
+
+def mouseReleased():
+    global selected_v, u
+    if selected_v:
+        for v in grid.keys():
+            if mouse_near(v):
+                grid[selected_v], grid[v] = grid[v], grid[selected_v]
+                u = recalculate_sizes_from_v_deg(graph, grid)
+    selected_v = None
+
+
+# TODO IDEAS:
+# Find distance outliers and try to shuffle them closer
+# Run many times without visualisation on Python 3 to get some huge samples

README.md

@@ -22,6 +22,12 @@
 
 ---
 
+![sketch_2020_08_18a](2020/sketch_2020_08_18a/sketch_2020_08_18a.png)
+
+[sketch_2020_08_18a](https://github.com/villares/sketch-a-day/tree/master/2020/sketch_2020_08_18a) [[Py.Processing](https://villares.github.io/como-instalar-o-processing-modo-python/index-EN)]
+
+---
+
 ![sketch_2020_08_17a](2020/sketch_2020_08_17a/sketch_2020_08_17a.png)
 
 [sketch_2020_08_17a](https://github.com/villares/sketch-a-day/tree/master/2020/sketch_2020_08_17a) [[Py.Processing](https://villares.github.io/como-instalar-o-processing-modo-python/index-EN)]

admin_scripts/s.py

@@ -0,0 +1,10 @@
+palavra = "Heineken"
+palavra_invertida = "" # começa vazia
+for letra in palavra:
+    # soma letra da palavra uma por uma
+    # formando string invertido
+    palavra_invertida = letra + palavra_invertida
+    
+print(palavra_invertida)
+
+print(reversed(palavra))