Useful links:
Datatypes
| Data Type |
Description |
Examples |
| Integers |
Whole Numbers |
-2, -1, 0, 1, 2, 3, 4, 5 |
| Floating-point numbers |
Numbers with decimal point |
-1.25, -1.0, β0.5, 0.0, 0.5, 1.0, 1.25 |
| Strings |
Ordered sequence of characters |
βaβ, βaaβ, βaaaβ, βHello!β, β11 catsβ |
| List |
Ordered sequence of objects |
[10, βHelloβ, 20.3] |
| Dictonary |
Unordered key : value pairs |
{βMyKeyβ : βValueβ} |
| Tuples |
Ordered immutable sequence of objects |
(10, βHello, 20.3) |
| Set |
Unordered collection of unique objects |
{βaβ, βbβ} |
| Bool |
Logical value indicating True or False |
True / False |
Variables
You can name a variable anything as long as it obeys the following rules:
- It can be only one word.
- It can use only letters, numbers, and the underscore (_) character.
- It canβt begin with a number.
- Variable name starting with an underscore (_) are considered as βunuseful`.
Example:
>>> spam = 'Hello'
>>> spam
'Hello'
Operators
| Operators |
Operation |
Example |
** |
Exponent |
2 ** 3 = 8 |
% |
Modulus/Remaider |
22 % 8 = 6 |
// |
Integer division |
22 // 8 = 2 |
/ |
Division |
22 / 8 = 2.75 |
* |
Multiplication |
3 * 3 = 9 |
- |
Subtraction |
5 - 2 = 3 |
+ |
Addition |
2 + 2 = 4 |
Comparison Operators
a = 3
b = 4
| Operators |
Operation |
Example |
> |
If the value of left operand is greater than the value of right operand, the condition becomes true |
(a > b) -> False |
< |
If the value of left operand is less than the value of right operand, the condition becomes true. |
(a < b) -> True |
== |
If the values of two operands are equal, then the condition becomes true. |
(a == b) -> False |
>= |
If the value of left operand is greater than or equal to the value of right operand, then condition becomes true. |
(a >= b) -> False |
<= |
If the value of left operand is less than or equal to the value of right operand, then condition becomes true. |
(a <= b) -> True |
!= |
If values of two operands are not equal, then condition becomes true. |
(a != b) -> True |
If - elif - else statements
Definition:
if my_condition is equal a value:
execute some code
elif my_other_condition is equal another value:
execute something different
else:
do something else
While loop
Definition:
- repeats statment(s) while a condition is TRUE
- requires an exit condition
while some_boolean_condition:
do something
else:
do something different
Example:
break_condition = 0
while break_condition < 10:
break_condition = break_condition + 1
print(break_condition)
else:
print("out of while loop")
For loop
- iterating over items of a sequence (usually a list)
mylist = [1,2,3,4,5,6,7,8,9,10]
for item in mylist:
print(item)
- iterating over numbers in range()
for i in range(0, 10, 2):
print(i)
- iterating over characters in a string
for letter in "Python":
print("current letter: ", letter)
- iterating over every key in a dictonary
d = {"k1":1, "k2":2, "k3":3}
for item in d:
print(item)
print(len(pets))
print(list(range(len(pets))))
for index in range(0,len(pets)):
print(index, pets[index])
- index and objects in list
for p,x in enumerate(pets):
print(p, x)
- BREAK: Breaks out of the current closest enclosing loop
- CONTINUE: Goes to the top of the closest enclosing loop
- PASS: Does nothing at all
while True:
print('Who are you?')
name = input()
if name != 'Joe':
continue
print('Hello, Joe. What is the password? (It is a fish.)')
password = input()
if password == 'swordfish':
break
print('Access granted.')
Lists
- Unlike strings, they are mutable
- elements inside a list can be changed
>>> spam = ['cat', 'bat', 3, 'elephant']
>>> spam
['cat', 'bat', 'rat', 'elephant']
>>> len(spam)
4
>>> spam = ['cat', 'bat', 3, 'elephant']
>>> spam[2]
'2'
>>> spam[-1]
'elephant'
>>> spam = ['cat', 'bat', 3, 'elephant']
>>> spam[0:4]
['cat', 'bat', 3, 'elephant']
>>> spam[1:3]
['bat', 3]
>>> spam[:2]
['cat', 'bat']
>>> spam = spam + ['add new item']
>>> spam
['cat', 'bat', 3, 'elephant', 'add new item']
>>> spam = ['cat', 'bat', 3, 'elephant']
>>> spam.append('append me!')
>>> spam
['cat', 'bat', 3, 'elephant', 'append me!']
Dictionaries
- unordered mappings of stored objects by using a key-value pairing (lists store objects in ordered sequence, can therefore be indeced or sliced)
- key value: allows to grab an object without knowing the index location
- {key1:value1, key2:value2} the key itself should always be a string
Definition:
>>> my_dict = {'key1':'value1', 'key2':'value2', 'key3':'value3'}
>>> my_dict
{'key1': 'value1', 'key2': 'value2', 'key3':'value3'}
>>> my_dict['key1']
'value1'
Example:
>>> prices_lookup = {'apples': 2.99, 'oranges': 1.89}
>>> prices_lookup['apples']
2.99
d.keys(): giving all the key inputs
>>> key = {'color': 'pink', 'age': 22}
>>> for k in key.keys():
>>> print(k)
color
age
d.values(): giving all the values
>>> value = {'color': 'pink', 'age': 22}
>>> for v in value.values():
>>> print(v)
pink
22
d.items(): giving the pairings - (result is also a tuple as it is in ())
>>> item = {'color': 'pink', 'age': 22}
>>> for i in item.items():
>>> print(i)
('color', 'pink')
('age', 22)
Functions
- for creating a clean, repeatable code
- allow us to create blocks of code that can be easily executed many times
- without needing to constantly rewrite the entire block of code
Definition:
def name_of_function(name):
do something
Example:
>>> def print_hello():
>>> print("Hello")
>>> print_hello()
Hello
>>> def run_check(num,low,high):
>>> if num in range(low,high):
>>> print (f"{num} is in the range between {low} and {high}")
>>> run_check(5,2,7)
5 is in the range between 2 and 7
When creating a function using the def statement, you can specify what the return value should be with a return statement. A return statement consists of the following:
- The return keyword
- The value or expression that the function should return
Example:
- Write a function that computes the volume of a sphere given its radius.
- The volume of a sphere is given as \(\frac{4}{3} Οr^3\)
>>> import math
>>> def vol(rad=5):
>>> V = 4/3 * math.pi* rad**3
>>> return V
>>> vol()
523.5987755982989
Example:
- if word starts with a vowel, add βayβ to end
- if word does not start with a vowel, put first letter at the end, then add βayβ
>>> def latin(word):
>>> first_letter = word[0]
>>> if first_letter in "aeiou":
>>> pig_word = word + "ay"
>>> else:
>>> pig_word = word[1:] + first_letter + "ay"
>>> return pig_word
>>> latin("apple")
'appleay'
Classes
Dataclasses are python classes but are suited for storing data objects. This module provides a decorator and functions for automatically adding generated special methods such as __init__() and __repr__() to user-defined classes.
- Storing data and representing certain data type
- Comparing to other objects of the same type
self
- representing the instance of a class
- accessing the attributes and methods of the class in python
__init__()
- A reseved method in python classes
- Called as constructor in object oriented terminology: Called when an object is created from a class and allows the class to initialize the attributes of the class
Example:
>>> class Vehicle():
>>> def __init__(self, colour, nb_wheels, name):
>>> self.colour = colour
>>> self.nb_wheels = nb_wheels
>>> self.name = name
>>> vehicle_1 = Vehicle("blue", 2, "bike")
>>> vehicle_2 = Vehicle("red", 4, "car")
>>> print("This is a " + vehicle_1.colour + " " + vehicle_1.name + " with ", vehicle_1.nb_wheels, " " + "wheels")
This is a blue bike with 2 wheels
>>> print("This is a " + vehicle_2.colour + " " + vehicle_2.name + " with " + str(vehicle_2.nb_wheels) + " " + "wheels")
This is a red car with 4 wheels
Example:
- Find out the cost of a rectangular field with breadth(b=120), length(l=160). It costs x (2000) rupees per 1 square unit:
>>> class Rectangle:
>>> def __init__(self, length, breadth, unit_cost=0):
>>> self.length = length
>>> self.breadth = breadth
>>> self.unit_cost = unit_cost
>>> def get_area(self):
>>> return self.length * self.breadth
>>> def calculate_cost(self):
>>> area = self.get_area()
>>> return area * self.unit_cost
>>> r = Rectangle(160, 120, 2000)
>>> print("Area of Rectangle: %s sq units" % (r.get_area()))
Area of Rectangle: 19200 sq units
Import
- getting access to code from another module by importing file/function
- import module_name:
>>> import math
>>> print(math.pi)
3.141592653589793
- import module_name.member_name
>>> from math import pi
>>> print(pi)
3.141592653589793
- import COMPAS in Grasshopper
In Grasshopper, COMPAS is imported from within a GhPython component. To verify that everything is working properly, simply create a GhPython component on your Grasshopper canvas, paste the following script and hit OK
import compas
from compas.datastructures import Mesh
from compas_ghpython.artists import MeshArtist
mesh = Mesh.from_obj(compas.get('faces.obj'))
artist = MeshArtist(mesh)
a = artist.draw_mesh()