L-System Turtle Graphics

import math
import turtle
t = turtle.Turtle()

'''
defaultRules = {
    'F': [t.fd, segLen],
    'B': [t.bk, segLen],
    'f': [fd, segLen],
    'b': [bk, segLen],
    '-': [lt, ang],
    '+': [rt, ang],
    '[': [push],
    ']': [pop],
    '?': [peek],
    '0': [t.pu],
    '1': [t.pd]
}
'''

def setup():
    t.ht()
    t.tracer(rate)
    t.width(thickness)
    t.speed(speed)
    t.rt(tilt)

def Lsystem(axiom, rules, iterations=1):
    result = "";
    for i in range(iterations):
        for c in axiom:
            if c in rules:
                result += rules[c]
            else:
                result += c
        axiom = result
        result = ""
    return axiom
def drawPath(path, rules):
    for c in path:
        if c in rules:
            rules[c][0](*rules[c][1:len(rules[c])])
    t.tracer(1)
def dPath(path, rules):
    for c in path:
        if c not in rules:
            continue
        if isinstance(rules[c], list):
            for rule in rules[c]:
                eval(rule)
        else:
            eval(rules[c])

    t.tracer(1)

def fd(len):
    t.pu()
    t.fd(len)
    t.pd()
def bk(len):
    t.pu()
    t.bk(len)
    t.pd()
def lt(a):
    t.speed(speed*5)
    t.lt(a)
    t.speed(speed)
def rt(a):
    t.speed(speed*5)
    t.rt(a)
    t.speed(speed)
def seth(h):
    tHead = t.heading()
    t.write((h-tHead) % 180)
    rt((tHead-h) % 360)

stack = []
def push():
    pos = [t.pos(), t.heading()]
    stack.append(pos)
def pop():
    penDown = t.isdown()
    pos = stack.pop()
    t.pu()
    t.speed(0)
    t.seth(pos[1])
    t.goto(pos[0])
    t.speed(speed)
    if isDown:
        t.pd()
def peek():
    penDown = t.isdown()
    pos = stack[-1]
    t.speed(0)
    t.seth(pos[1])
    t.goto(pos[0])
    t.speed(speed)
    if isDown:
        t.pd()

def branch():
    t.fd(segLen)


def main(fill = False):
    global ang,segLen,iters,speed,rate,tilt,thickness

    tilt = 0
    thickness = 1
    rate = 1
    speed = 3
    iters = 0
    segLen = 10
    ang = 45

    setup()
    t.pu()
    t.goto(0, 0)
    t.pd()

    path = Lsystem('0', {
        '0': '1[0]0',
        '1': '11'
    }, iters)

    if fill:
        t.begin_fill()
    dPath(path, {
        '0': ['t.fd(segLen)', 't.rt(90)', 't.circle(segLen/2)'],
        '1': 't.fd(segLen)',
        '[': ['push()', 't.lt(ang)'],
        ']': ['pop()', 't.rt(ang)']
    })
    """
    drawPath(path, {
        '0': [leaf],
        '1': [branch],
        '[': [push],
        ']': [pop]
    })
    """
    t.end_fill()

main()