The print() function prints things on the screen. To use it, type print().Then put two double quotes or single quotes between the parentheses. In the quotes, type a word. The print() function can have multiple parameters.
Example
>>> print("Hello world ")
Hello world
>>> print(242)
242
The input function gets input from a user. It can have only one parameter. The string inside the parenthesis is what is printed out.
Example
>>> x = input("Type something:")
Type something:5
>>> print(x)
5
The quit() function quits python
>>> quit()
A number without decimals is an integer. In python it is called an int.
Example
>>> x = 5
>>> print(x)
5
A number with decimals is a called a float.
Example
>>> x = 5.5
>>> print(x)
5.5
A string is a string of characters. Strings can include any character.
Example
>>> x = "Hello world 123^!(*@:+_-"
>>> print(x)
Hello world 123^!(*@:+_-
Strings can be added to create bigger strings
>>> x = "63"
>>> y = "37"
>>> z = x + y
>>> print(z)
6337
Some characters need to have a backslash to work
print("Hello world\t")
That will print a tab
\n prints a newline
\\ prints a backslash
To convert an int to a float, the keyword is float
>>> x = 17
>>> print(float(x))
17.0
To convert a float to an int, the keyword is int. Since it is an int, it is rounded down.
>>> x = 17.23
17
The keyword for strings is str
>>> print(str(23))
23
Formats are used to embedd variables into strings.
x = 5
print("x is equal to %s" % x)
A boolean is a variable that is either true or false.
>>> x = True
>>> y = False
>>> print(x)
True
>>> print(y)
False
The bool function decides whether a value is true or false. It is useful for input validation.
>>> print(bool(0))
False
>>> print(bool(1))
True
None is type without any value.
>>> a = None
>>> print(a)
None
Unlike strings, floats and ints can be added to get a sum.
>>> x = 63
>>> y = 37
>>> z = x + y
>>> print(z)
100
You can also subtract, multiply, or divide numbers.
>>> a = 687 + 274
>>> b = 1000 - 39
>>> c = 31 * 31
>>> d = 3844 / 4
>>> print(str(a) + str(b) + str(c) + str(d))
961961961961
You can also use exponent.
>>> 31**2
961
The modulo operator finds the remainder.
>>> 962 % 31
1
The order of assignment operations is (), **, %, /, *, +, -
A list is a collection of different datatypes that are stored in one variable
>>> a = [12, "12str", True, "true"]
>>> print(a)
[12, '12', True, 'True']
The name has index values starting from 0. To access an individual item from a list put the name of the list and in between square brackets put the index value
>>> print(a[3])
true
A tuple is a similar to a list. It uses parenthesis instead of square brackets.
>>> b = (412, 1256, 67, 5, bool(None))
>>> print(b(4))
>>> True
You cannot change items in a tuple.
Dictionaries are lists with multiple named variables inside it instead of index numbers.
Dictionaries consists of key:value pairs.
>>> c = {"ca": 1, "cb": 2, "cc": 3, "cd": 4, "ce": 5}
>>> print(c["cc"])
3
>>> d = {"ca": "row", "cb": "bow", "cc": "tow", "cd": "low", "ce": "joe"}
>>> print(c["ca"])
row
Another way of using a dictionary is the dict() function.
>>> d = dict(da=1, db=2, dc=3, dd=4, de=5)
Comparison operators compare numbers. They return a boolean.
>>> 5 != 6
True
>>> 4 + 4 == 8
True
== and != check whether 2 values are equal or not.
This is a condition.
> and < check whether a number is greater or less than another number.
>>> 5 > 6
False
>>> 6 < 7
True
<= and >= check whether the number is greater than or equal to or less than or equal to
logical operators test more than one condition.
The or operator tests whether one of the conditions is true. The and operator tests whether both conditions are true
>>> 5 == 6 or 4 == 4
True
>>> 5 == 6 and 4 == 4
False
The order of logical operations is: brackets, and, or.
>>> 5 == 6 and (4 == 4 or 5 == 3) and 2 == 4
False
An if statement runs code only if a condition is true.
if 10 == 9 or 4 == 4:
print("4 equals 4")
4 equals 4
The else runs if the condition is not true.
if 10 == 9 and 4 == 4:
print("Condition is true")
else:
print("10 does not equal 9")
10 does not equal 9.
elif runs a piece of code depending on a different condition if the first condition isn't true.
if 3 > 5:
print("first is true.")
elif 3 > 2:
print("second is true")
else:
print("none are true")
second is true
The for loop runs a piece of code depending on an integer.
for variable in range(5):
print("hello")
hello
hello
hello
hello
hello
The while loop runs a piece of code while a condition is met.
x = 5
while x >= 0:
print("hello")
x = x - 1
hello
hello
hello
hello
hello
break will quit the control structure.
continue will continue the control structure.
while True:
print("hello")
if 5 != 5:
continue;
else:
break;
hello
A module is a group of related functions and classes. It is also known as a library
The import statement accesses a module.
The math module has math functions
>>> import math
Now the program has access to math functions such as square root and pow.
>>> import math
>>> print(math.sqrt(64))
8
>>> math.pow(2, 3)
8
The time module has time functions
>>> import time
>>> time.sleep(5)
>>>
The computer paused for 5 seconds.
>>> print(time.asctime())
Tue May 1 07:41:23 2018
>>> print(time.time())
1525309467.8433716
prints the time from 1970.
Functions are groups of code.
def calculate():
print(13 + 13)
...
calculate()
26
Functions with parameters need extra information to run.
def calculate(x, y):
print(x, y)
calculate(13, 13)
26
The print function has 1 or more parameters
Parameters can have variable declarations
calculate(x=5, y=6)
11
Return returns a value
def calculate(x, y):
z = (x + y) * 3
return z
x = calculate(x=7, y=9)
print(x)
16
An object is a collection of related variables and functions
The math object has it's own variable called pi.
import math
>>> math.pi
3.141592936
It also has a function such called sqrt()
>>> math.sqrt(25)
5
The subprocess object has functions for the console.
import subprocess
subprocess.call('clear', shell=True)
The shell will clear now
Constants are variables that cannot change. Constants in python are in capital letters. Constants are declared in the beginning of the program
CONSTANTEXAMPLE = "Hello"
A class is a blueprint for an object. The name of a class usually starts with a capital letter. All classes in python have an __init__() function to declare the variables. Every function has a self parameter.
class Dog:
def __init(self, breed, color, size):
self.breed = breed
self.color = color
self.size = size
breed, color, and size are properties(information) of the Dog class. This is how to create an object of the Dog class.
a = Dog(breed="beagle", color="black", size=65)
print(a.breed)
beagle
print(a.color)
black
print(a.size)
65
Methods are the functions of the class. The functions must have a self parameter.
class Dog:
def __init(self, breed, color, size):
self.breed = breed
self.color = color
self.size = size
def eat(self):
print("Munch munch")
a = Dog(breed="grayhound", color="gray", size=125)
a.eat()
Munch munch