int, float, complexforif/else/elifwhileClasses, Objects, and Instances
Short version: Python 2.x is legacy, Python 3.x is the present and future of the language final
A Python interactive mode makes it easy to test short snippets of code, but there are also a bunch of editors like Sublime Text available as well as bundled development environments IDEs like PyCharm.
We will use:
You could use:
Analogy: Blueprint of a house
Example: the data type integer is a class
a = 5) makes an instance (object) of class inta is a reference to this objectint has methods defined, for example bit_length()'This is a String' ) or multiline (''' This is a String...''' )my_string[2] == 'i'#create string
typo_str = 'Peeface'
#Oh no... a typo, not a good way to start a book, so change it
typo_str[1] = 'r'
---------------------------------------------------------------------------
TypeError Traceback (most recent call last)
<ipython-input-18-a40cf4edfc3f> in <module>()
----> 1 typo_str[1] = 'r'
TypeError: 'str' object does not support item assignment
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# print something
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print(c)
list_a = [5, 3.0, 'Hello']0list_a[2] would give 'Hello'#creating the list
list_a = [5, 3.0, 'Hello']
#extract third element/object and create reference to it
hello_str = list_a[2]
#mutate list
list_a[2] = 'Good bye'
#print new list
print(list_a)
[5, 3.0, 'Good bye']
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# what is hello_str
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# reverse indexing
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# stepwise indexing (start:stop:step)
tuple_a = (5 , 3.0, 'Hello')#create tuple
tuple_a = (5, 3.0, 'Hello')
#extract third element/object and create reference to it
hallo_str = tuple_a[2]
#mutate it???
tuple_a[2] = 'Good bye'
---------------------------------------------------------------------------
TypeError Traceback (most recent call last)
<ipython-input-16-2ae0e9084ab6> in <module>()
----> 1 tuple_a[2] = 'Good bye'
TypeError: 'tuple' object does not support item assignment
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my_dict = {'one':1, 'two':2, 'three':3}
print(my_dict['one'])
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# how to test if certain key is in dict
print('one' in my_dict)
print('four' in my_dict)
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### example immutable
x = 10
y = x
x = x + 1
print('y: ',y)
### example mutable
x_l = ['10']
y_l = x_l
x_l.append('11')
print('y_l: ', y_l)
True or False as result= is an assignment, == is the comparison operatorand, or and notfor Loopthe for loop is used to iterate over a sequence
for x in y:
counter = counter +1
Loop continues until it reaches last item in y
Example: Sum of numbers
# List of numbers
numbers = [6, 5, 3, 8, 4, 2, 5, 4, 11]
# variable to store the sum
sum = 0
# iterate over the list
for val in numbers:
sum = sum + val
if/elif/elseif x == 2: # expression
print(my_string) # statement
True, statements will be executedif x == 2: # expression
print(my_string) # body of if
else:
print(your_string) # body of else
True, statement in body of if will be executed, otherwise statement in body of else will be executedif x == 2: # 1st expression
print(my_string) # body of if
elif x == 3: # 2nd expression
print(our_string) # body of elif
else:
print(your_string) # body of else
elif is short for else ifTrue, statement in body of if will be executed, otherwise 2nd expression will be checked and so on...while Loopwhile iterates over a block of code, as long as a statement is TrueIs used when the number of times the loop has to be executed is not known beforehand (compare: for loop)
while x < 2: # expression
print(our_string)
expression is checked before entering the loop for the first time
def my_statement_printer(statements):
"""This is my docstring:
Function to print my statements"""
for statement in statements:
print('I think ' + statement)
def is the keyword for the function definitionreturn statement, if no return value is given the function returns Nonedef add(num1,num2):
"""This function adds two numbers"""
return num1 + num2
print(add(2,3))
print(add.__doc__)
return statement exits a functionA variable defined inside a function is not visible outside the function
def func():
x = 10
print(x)
---------------------------------------------------------------------------
NameError Traceback (most recent call last)
<ipython-input-3-fc17d851ef81> in <module>()
----> 1 print(x)
NameError: name 'x' is not definedx inside func is not visible outside, so they can have the same namex inside func is a local variable inside the function def add(num1,num2=1):
"""This function adds two numbers, if no second number is defined it adds one to num1."""
return num1 + num2
As already mentioned everything, that means every thing in python is an object. An object is an instance of a class, which defines which attributes and methods an object holds.
class is the keyword for class definitionclass holds attributes (data and methods)dir argument one can list all methods of an object
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y = 5
dir(y)
y is not only a number, it has a lot of methods which we can use
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print(y.bit_length())
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import time
class MinimalCake:
def __init__(self, eier=2, mehl=500, milch=250):
self.eggs = eier
self.flour = mehl
self.milk = milch
self.stirred = False
def stir(self):
print('stirring...')
time.sleep(2)
print('...dough')
self.stirred = True
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one_minimal_cake = MinimalCake()
print(one_minimal_cake.eggs, one_minimal_cake.stirred)
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one_minimal_cake.stir()
print(one_minimal_cake.stirred)
Ok, we have dough. But it really doesn't taste well and it can't be baked... That's a disaster, we want choclate and sugar!!
Question: Is a MinimalCake object mutable or immutable?
Please write another class which holds attributes for choclate, sugar and whatever you want. Further, we should be able to bake it. But attention!!! If it is not stirred, baking it would be a waste.
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