python notes

# variables
name = "Evaldo"
age = 27

# output
print(name)
print(age)

# strings
'Evaldo'
"Evaldo"
'evaldo\'s'
'evaldo is {}'.format(age)
'''
evaldo 
    is
         27'''
"""
evaldo 
    is
         27"""
         
# lists
# strings are lists like
name = "Evaldo"
name[1] -> returns 'v'

l = [1,2,3,4]
l[-1] -> returns 4

>>> [1,2]+[3,4]
[1, 2, 3, 4]

>>> "hello"+"world"
'helloworld'

>>> "Hello"*2
'HelloHello'

>>> [1,2]*2
[1, 2, 1, 2]

>>> a = [1,2]
>>> a.append(3)
>>> a
[1, 2, 3]

>>> a.append([4,5])
>>> a
[1, 2, 3, [4, 5]]

>>> a.remove([4,5])
>>> a
[1, 2, 3]

>>> a.extend([4,5])
>>> a
[1, 2, 3, 4, 5]

>>> del a[0]
>>> a
[2, 3, 4, 5]

# booleans
False
True
# everything that does't have a value or is empty is falsy
bool([]) -> return False
bool("") -> return False
bool(None) -> return False
bool([1,2,3]) -> return True
bool("Evaldo") -> return True

# boolean operations
==
!=
# in python we don't have 'coercion' operators, ===, !==
>, <, >=, <=, in

>>> 5 in [1,2,3,4,5]
True
>>> 6 in [1,2,3,4,5]
False
>>> "cheese" in "cheeseshop"
True

is -> tests if two objects have the same reference
1 is 1
>>> True
>>> a = "Evaldo"
>>> b = "Evaldo"
>>> a is b
True
>>> [1,2] is [1,2]
False
>>> "Evaldo" is "Evaldo"
True

>>> not True
>>> False
>>> not False
>>> True

# if/else/operators
>>> days_open = ['Monday','Tuesday','Wednesday','Thursday']
>>> today = 'Tuesday'
>>> if today in days_open:
...     print("come on in!")
... else:
...     print("Sorry, we're closed")
... 
come on in!

>>> if today not in days_open:
...     print("Sorry, we're closed")
... 
Sorry, we're closed

# Loops
>>> a = [1,2,3,4]
>>> while a:
...    print a[0]
...    del a[0]
... 
1
2
3
4

>>> for a in [1,2,3,4]:
...     print a
... 
1
2
3
4

>>> for a in [1,2,3,4]:
...     if a < 3:
...         continue
...     print a
... 
3
4

>>> for a in [1,2,3,4]:
...     if a > 3:
...         break
...     print a
... 
1
2
3

>>> while a:
...     print a
...     a -= 1
... else:
...     print("finished")
... 
10
9
8
7
6
5
4
3
2
1
finished

>>> for a in [1,2,3,4]:
...     print a
... else:
...     print("finished")
... 
1
2
3
4
finished

# To use else with for/while loops the loop can't throw exceptions or have break
>>> for a in [1,2,3,4]:
...     if a > 2:
...         break
...     print a
... else:
...     print("finished")
... 
1
2

# Input / Output
>>> age = input("what's your age? ") 
what's your age? 28
>>> age
'28'
>>> age + 1
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: must be str, not int

>>> age = int(input("what's your age? "))
what's your age? 28
>>> age+1
29

>>> print(age)
28

# functions
def even(num):
    if num % 2 == 0:
        return True
    else:
        return False

# Exceptions (the exception to the rule)
try:
    speed = int(input("What is the airspeed velocity of an unladen swallow? "))
except ValueError:
    print("What? I don't kno-oooooooooooooooo!")
else:
    print("I think a swallow could go faster than {}.".format(speed))