add mergesort python def.py

#!/usr/bin/env python3
"""

         sorting_animation.py

A minimal sorting algorithm animation:
Sorts a shelf of 10 blocks using insertion
sort, selection sort and quicksort.

Shelfs are implemented using builtin lists.

Blocks are turtles with shape "square", but
stretched to rectangles by shapesize()
 ---------------------------------------
       To exit press space button
 ---------------------------------------
"""
from turtle import *
import random


class Block(Turtle):

    def __init__(self, size):
        self.size = size
        Turtle.__init__(self, shape="square", visible=False)
        self.pu()
        self.shapesize(size * 1.5, 1.5, 2) # square-->rectangle
        self.fillcolor("black")
        self.st()

    def glow(self):
        self.fillcolor("red")

    def unglow(self):
        self.fillcolor("pink")

    def __repr__(self):
        return "Block size: {0}".format(self.size)


class Shelf(list):

    def __init__(self, y):
        "create a shelf. y is y-position of first block"
        self.y = y
        self.x = -150

    def push(self, d):
        width, _, _ = d.shapesize()
        # align blocks by the bottom edge
        y_offset = width / 2 * 20
        d.sety(self.y + y_offset)
        d.setx(self.x + 34 * len(self))
        self.append(d)

    def _close_gap_from_i(self, i):
        for b in self[i:]:
            xpos, _ = b.pos()
            b.setx(xpos - 34)

    def _open_gap_from_i(self, i):
        for b in self[i:]:
            xpos, _ = b.pos()
            b.setx(xpos + 34)

    def pop(self, key):
        b = list.pop(self, key)
        b.glow()
        b.sety(200)
        self._close_gap_from_i(key)
        return b

    def insert(self, key, b):
        self._open_gap_from_i(key)
        list.insert(self, key, b)
        b.setx(self.x + 34 * key)
        width, _, _ = b.shapesize()
        # align blocks by the bottom edge
        y_offset = width / 2 * 20
        b.sety(self.y + y_offset)
        b.unglow()


    def pop_without_closing_gap(self, key):
        #b = list.pop(self, key)
        b = self[key]
        b.glow()
        b.sety(200)
        #self._close_gap_from_i(key)
        return b

    def insert_without_opening_gap(self, key, b):
        #self._open_gap_from_i(key)
        #list.insert(self, key, b)
        self[key] = b
        b.setx(self.x + 34 * key)
        width, _, _ = b.shapesize()
        # align blocks by the bottom edge
        y_offset = width / 2 * 20
        b.sety(self.y + y_offset)
        b.unglow()



def isort(shelf):
    length = len(shelf)
    for i in range(1, length):
        hole = i
        while hole > 0 and shelf[i].size < shelf[hole - 1].size:
            hole = hole - 1
        shelf.insert(hole, shelf.pop(i))
    return

def ssort(shelf):
    length = len(shelf)
    for j in range(0, length - 1):
        imin = j
        for i in range(j + 1, length):
            if shelf[i].size < shelf[imin].size:
                imin = i
        if imin != j:
            shelf.insert(j, shelf.pop(imin))

def partition(shelf, left, right, pivot_index):
    pivot = shelf[pivot_index]
    shelf.insert(right, shelf.pop(pivot_index))
    store_index = left
    for i in range(left, right): # range is non-inclusive of ending value
        if shelf[i].size < pivot.size:
            shelf.insert(store_index, shelf.pop(i))
            store_index = store_index + 1
    shelf.insert(store_index, shelf.pop(right)) # move pivot to correct position
    return store_index

def qsort(shelf, left, right):
    if left < right:
        pivot_index = left
        pivot_new_index = partition(shelf, left, right, pivot_index)
        qsort(shelf, left, pivot_new_index - 1)
        qsort(shelf, pivot_new_index + 1, right)

def msort(shelf,start_pos,end_pos):
    if start_pos == end_pos:
        return shelf[start_pos:end_pos+1]
    l = end_pos - start_pos + 1
    h1 = msort(shelf, start_pos, start_pos+l//2-1)
    h2 = msort(shelf, start_pos+l//2, end_pos)
    return merge(shelf, h1, h2, start_pos)

def randomize():
    disable_keys()
    clear()
    target = list(range(10))
    random.shuffle(target)
    for i, t in enumerate(target):
        for j in range(i, len(s)):
            if s[j].size == t + 1:
                s.insert(i, s.pop(j))
    show_text(instructions1)
    show_text(instructions2, line=1)
    enable_keys()

def show_text(text, line=0):
    line = 20 * line
    goto(0,-250 - line)
    write(text, align="center", font=("Courier", 16, "bold"))

def start_msort():
    disable_keys()
    clear()
    show_text("Merge Sort")
    qsort(s, 0, len(s) - 1)
    clear()
    show_text(instructions1)
    show_text(instructions2, line=1)
    enable_keys()


def start_ssort():
    disable_keys()
    clear()
    show_text("Selection Sort")
    ssort(s)
    clear()
    show_text(instructions1)
    show_text(instructions2, line=1)
    enable_keys()

def start_isort():
    disable_keys()
    clear()
    show_text("Insertion Sort")
    isort(s)
    clear()
    show_text(instructions1)
    show_text(instructions2, line=1)
    enable_keys()

def start_qsort():
    disable_keys()
    clear()
    show_text("Quicksort")
    qsort(s, 0, len(s) - 1)
    clear()
    show_text(instructions1)
    show_text(instructions2, line=1)
    enable_keys()


def merge(shelf,h1,h2,h1_offset):
    h1_pos = h2_pos = r_pos = 0
    n = len(h1)+len(h2)
    r = [None]*n
    for i in range(0,n):
        if h1_pos == len(h1):
            r[r_pos] = h2[h2_pos]
            h2_pos +=1
        elif h2_pos == len(h2):
            r[r_pos] = h1[h1_pos]
            h1_pos += 1
        else:
            if h1[h1_pos].size < h2[h2_pos].size:
                r[r_pos] = h1[h1_pos]
                h1_pos += 1
            else:
                r[r_pos] = h2[h2_pos]
                h2_pos += 1
        r_pos += 1

    visualize_merge(shelf,r,h1_offset)
    return r

def visualize_merge(shelf,r,offset):
    b = [None]*len(r)
    for j in range(0,len(r)):
        for i in range(0,len(shelf)):
            if shelf[i] == r[j]:
                b[j] = shelf.pop_without_closing_gap(i)
                break
    for j in range(0,len(r)):
        shelf.insert_without_opening_gap(offset+j, b[j])


def init_shelf():
    global s
    s = Shelf(-200)
    vals = (4, 2, 8, 9, 1, 5, 10, 3, 7, 6)
    for i in vals:
        s.push(Block(i))

def disable_keys():
    onkey(None, "m")
    onkey(None, "s")
    onkey(None, "i")
    onkey(None, "q")
    onkey(None, "r")

def enable_keys():
    onkey(start_msort, "m")
    onkey(start_isort, "i")
    onkey(start_ssort, "s")
    onkey(start_qsort, "q")
    onkey(randomize, "r")
    onkey(bye, "space")

def main():
    getscreen().clearscreen()
    ht(); penup()
    init_shelf()
    show_text(instructions1)
    show_text(instructions2, line=1)
    enable_keys()
    listen()
    return "EVENTLOOP"

instructions1 = "press i for insertion sort, s for selection sort, q for quicksort, m for merge sort"
instructions2 = "spacebar to quit, r to randomize"

if __name__=="__main__":
    msg = main()
    mainloop()