Skills, Tactics, Plays

Python Overview

Using Python

$ python3
Python 3.5.3 (default, Jan 19 2017, 14:11:04)
[GCC 6.3.0 20170118] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> print("Hello RoboCup!")
Hello RoboCup!

Basic Syntax

# Hello world
print("Hello World!")

# Set a variable
myinteger = 1
mydouble = 1.0
mystr = "one"

print(myinteger)
print(mydouble)
print(mystr)

Hello World!
1
1.0
one

IF Statements and Conditionals

if True:
    print("RoboCup is great!")
if False:
    print("IGVC is great...")

if True:
    print("RoboCup is the best!")
elif True:
    print("RoboRacing is the best...")
else:
    print("IGVC is the best...")

a = 5
if a > 2:
    print("a is greater than 2!")
if a > 2 and a < 10:
    print("a is > 2 and < 10")
print("a is greater than 3" if a > 3 else "a is less than 3")
print("a is greater than 9" if a > 9 else "a is less than 9")

RoboCup is great!
RoboCup is the best!
a is greater than 2!
a is > 2 and < 10
a is greater than 3
a is less than 9

Loops and range()

a = 10
while a > 0:
    print(a, end=" ")
    a = a - 1
print("")

print(list(range(10)))
for i in range(10):
    print(i * i, end=" ")
print("")

10 9 8 7 6 5 4 3 2 1 
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
0 1 4 9 16 25 36 49 64 81 

Functions

def func1(a, b):
    return a + b

print(func1(2, 4))

# Lambda Expressions ('advanced' topic)
def secret_func():
    return "RoboCup!"
def welcome(target):
    return "Welcome to " + target()

print(welcome(secret_func))
print(welcome(lambda: "RoboJackets!"))
# Lambda with arguments
# print(welcome(lambda arg1, arg2: "RoboJackets!"))

6
Welcome to RoboCup!
Welcome to RoboJackets!

Object Oriented Python

class BaseClass():
    globalVar = 1
    # Constructor
    def __init__(self):
    print("Initializing a Base")
    self.local_var = 2

class ChildClass(BaseClass):
    def __init__(self):
    super().__init__() # call superclass constructor
    print("Initializing Child")
    print("Our local var is: " + str(self.local_var))

# When defining class methods, pass 'self' as the first arg.
# Self refers to the current class instance.
a = BaseClass()
print("---")
a = ChildClass()

Initializing a Base
---
Initializing a Base
Initializing Child
Our local var is: 2

Additional Python Resources

• lightbot - A Introduction to Programming Logic
• Python Beginner Hub
• Python Syntax Overview
• A intro to python

State Machines

What are they?

• A state machine is a series of states
• You can transition between them
• A state could have multiple transition
• A state transition only occurs if a condition is fulfilled

Examples

• A car engine is a state machine, each piston going between different internal states to move the car forward
• A washing machine is a state machine, going between different states to cycle between wash, dry, etc.
• Wikipedia Page on State Machines

Elevator

Move

Details

• Every Play starts in a 'start' state
• Most plays will instantly transition into a running state (in this case behavior::running)
• This particular play will go into behavior::completed once we reach a target position
• However, if we are ever bumped out of place, we are put back into the running state (to continue moving)
• Another thing to notice here is that every state here is a behavior::<thing> state.
  • These states are created by the state machine machinery we have set up.
  • They are used to determine whether a state can be killed or not, or if it is waiting for something
  • Most of the action will be done in a subclass of bheavior::running or behavior::running itself if you have a simple class.

Pass Receive

Details

• This example is a bit more complicated, as we have multiple running states
• Each one of these substates are classified as running by our machinery, since they subclass behavior::running
• A brief explanation is: if we are running, and the ball is ever kicked, immediately receive, but if we have some time, try to align yourself properly at the designated receive coordinate.

Passing

Details

• Here we have more running substates
• A pass is fairly linear, as it has preparing -> kicking -> receiving states
• However, if we 'timeout' in the preparing or kicking states, we fail the current behavior
  • This can happen if our robot is ever stuck

Additional Information on State Machines

• While you do not need to know advanced state machine ideas, you need to be comfortable working with and parsing existing state machines from a diagram or from our code.
• Wikipedia Article
• A quick block post about state machines
• You might be using state machines in a hacky way already&x2026;
• Our Current State Machine Implementation

Plays, Tactics, Skills

• A Basic Unit in our AI
• Only one Play can run at a time

Skill

• Involves only one robot
• Extremely basic building blocks
• Examples
  • Move
  • Kick
  • Face a direction
  • Capture the ball
• Located in soccer/gameplay/skills/

Tactics

• Involves multiple robots
• Contains skills
• Can contain unique behavior (but usually not)
• Examples
  • Pass
  • Defend
  • Line Up
• Located in soccer/gameplay/tactics/

Plays

• Only one can run
• Contains tactics
• Examples
  • Basic122 (basic offense)
  • Two side attack (basic offense)
  • Stopped Play
  • Line Up
  • Corner Kick
• Located in soccer/gameplay/plays/*/

Notes

• Only plays are actually runnable in our model
  • If you want to run a tactic, make a dummy play that runs that tactic on startup
• For now, we'll only look at plays to keep things simple (maybe we'll get more complex later)

Basic Plays and State Machines

• Every Play is a State Machine as well!
• Plays use State Machines to tell them what to do
• This is a good thing, since we can have very complex behavior in a play

Defining States

# First create a state Enum (An enum is just a group of names)
class OurState(enum.Enum):
    start = 0
    processing = 1
    terminated = 2

# Then, register your states in our state machine class
# You must be in a play/tactic/skill for this to work
self.add_state(PlayName.OurState.start,
           # This is the superclass of our state. Most of the time,
           # this is 'running' (see below)
           behavior.Behavior.State.start)

self.add_state(PlayName.OurState.processing,
           behavior.Behavior.State.running)

self.add_state(PlayName.OurState.terminated,
           behavior.Behavior.State.completed)

Defining Transitions

self.add_transition(
    # Start state for this transition
    behavior.Behavior.State.start,
    # End state for this transition
    PlayName.OurState.processing,
    # Condition for this transition (Replace 'True' with a conditional)
    lambda: True,
    # Documentation String
    'immediately')

Defining Actions to Take In A State

# Assuming we have the PlayName.OurState.processing state

# Action taken when entering this state
def on_enter_processing(self):
    print("We have begun our processing")

# Action taken every frame we are in the processing state
def execute_processing(self):
    print("Processing is Ongoing")

# Action taken when we exit the processing state
def on_exit_processing(self):
    print("Processing is Completed!")

Your Assignment

• Create a play that prints out which half of the field the ball is currently in
• EX: Print out "TopHalf" when in the top half of the field, and "BottomHalf" otherwise.
• Use state machines to print this out ONLY ON A TRANSITION. (Don't simply print out every frame)
• Extra Credit: Can you come up with another cool thing to do with state machines?

Tips

• The field coordinates start at 0, 0; Which is our Goal.
• Field Size Docs: (http://bit.ly/2cLsUBL)
• Ball Position Docs: (http://bit.ly/2damxXA)
• Move the template starter from soccer/gameplay/plays/skel/which_half.py to soccer/gameplay/plays/testing
• Start by just printing the Y coordinate of the ball and work up from there

Useful Tools

# Gets the y position of the ball
main.ball().pos.y
# Gets the field length in meters
constants.Field.Length

Exercise Details

• Link to Starter File
• Ask on gitter for help and answers!

Answers

• Which Half Answers