Truthiness and None

Here is the None object.

>>> type(None)
<class 'NoneType'>

Here we cast to boolean to see the truthiness of objects.

>>> bool(1)
True
>>> bool(o)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'o' is not defined
>>> bool(0)
False
>>> bool(42)
True
>>> bool(-42)
True
>>> bool(0.0)
False
>>> bool(1.0)
True
>>> ##zero is falsy, nonzero is truthy
>>> bool("")
False
>>> bool("ewq")
True
>>> #empty strings are falsy
>>> bool([])
False
>>> bool([5])
True
>>> bool((1,2,3))
True
>>> bool(5,)
True
>>> bool((5,))
True

the symbol table is a dictionary of all variables and their values.

Before you make any variables, the symbol table consists of Python's linguisitic infrastructure.

>>> dir()
['__annotations__', '__builtins__', '__doc__', '__loader__', '__name__', '__package__', '__spec__']

Now make a variable and watch what happens. Our variable appears in the symbol table.

>>> x = 5
>>> dir()
['__annotations__', '__builtins__', '__doc__', '__loader__', '__name__', '__package__', '__spec__', 'x']

This is no surprise.

>>> y = 4
>>> print(x + y)
9

Here is the symbol table.

>>> dir()
['__annotations__', '__builtins__', '__doc__', '__loader__', '__name__', '__package__', '__spec__', 'x', 'y']

print and its Many Powers (§ 8)

# what does this do?
# this is the comment token
# python ignores everything from it to the end of the line.
print("Hello")
print(1,2,3, True, "cows", [1,2,3])
print(1,2,3, True, "cows", [1,2,3], sep = " * ")
print(1,2,3, True, "cows", [1,2,3], sep = "|")
print(1,2,3, True, "cows", [1,2,3], end = "FOO")
print("a", end="")
print("b", end="")
print("a", end="")
print("c", end="")
print("d", end="")

The Symbol Table and Expressions (§ 9)

When you create a variable you write on the symbol table.

Think of two ways or more that you can make the little triangle of stars

*
**
***
****
*****
******    

Here are the most straighforward solutions.

print("*")
print("**")
print("***")
print("****")
print("*****")
print("******")

print('''*
**
***
****
*****
******''')

These two are oily but cute.

#Ari E
print('*','**','***','****','*****','******', sep ='\n')

print("*\n**\n***\n****\n*****\n******")

Here comes the hotdog parade.

#Riley
for i in range(7):

    print("*" * i)

# Chris A
print('\n'.join(['*'*i for i in range(1, 7)]))

#Al Pagar
star = "*"
for i in range(6):
    print(star)
    star = star + "*"

Now try this.

      *
     * *
    * * *
   * * * * 
  * * * * * 
 * * * * * * 
     * *
     * *

Here are two easy ways.

#Ari E
print('''
      *
     * *
    * * *
   * * * *
  * * * * *
 * * * * * *
     * *
     * *''')

#Me
print(""      *")
print(""     * *")
print(""    * * *")
print(""   * * * *")
print(""  * * * * *")
print("" * * * * * *")
print(""     * *")
print(""     * *") 

This works but it's a wee bit gamy.

print("      *\n     * *\n    * * *\n   * * * *\n  * * * * *\n * * * * * *\n* * * * * * * \n     * *\n     * *")

Now the hotdogs come out to play!

for i in range(1,7): print(' '*(7-i), ' ', ('* '*i))
    
for i in range(1, 3): print(' '*7, '* *')

for i in range(1, 9):
    if i > 6:
        print(f'{"* *":^30}')
    else:
        spaced = ('* '*i).strip()
        print(f'{spaced:^30}')

print("      *\n     * *\n    * * *\n   * * * *\n  * * * * *\n * * * * * *\n* * * * * * * \n     * *\n     * *")