Review of fundamentals A

In this notebook, you will guess the output of simple Python statements. You should be able to correctly predict almost all (ideally all) of them. If you get something wrong, make sure you understand why! Don’t be satisfied until you’ve understood why every snippet of code returns the value it does or produces the error it does.

Simple operations

3 + 10

13

3 = 10

  File "<ipython-input-4-ac50e1f5290d>", line 1
    3 = 10
SyntaxError: can't assign to literal

3 == 10

False

3 ** 10

59049

'3 + 10'

'3 + 10'

3 * '10'

'101010'

a*10

---------------------------------------------------------------------------
NameError                                 Traceback (most recent call last)
<ipython-input-9-ee62d7991d84> in <module>()
----> 1 a*10

NameError: name 'a' is not defined

'a' * 10

'aaaaaaaaaa'

int('3') + int('10')

13

int('hello world')

---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-12-1e75bebcb0a1> in <module>()
----> 1 int('hello world')

ValueError: invalid literal for int() with base 10: 'hello world'

10 / 5

2

10 / 4

2

float(10 / 4)

2.0

float(10)/4

2.5

type("True")

str

type(True)

bool

Conditionals

a=3
if (a==3):
    print("it's a three!")

it's a three!

a=3
if a==3:
    print("it's a four!")

it's a four!

a=3
if a=4:
    print( "it's a four!")
    

  File "<ipython-input-21-5b9cab591576>", line 2
    if a=4:
        ^
SyntaxError: invalid syntax

a=3
if a<10:
    print ("we're here")
elif a<100:
    print( "and also here")
    

we're here

a=3
if a<10:
    print("we're here")
if a<100:
    print("and also here")
    

we're here
and also here

a = "True"
if a:
    print ("we're in the 'if'")
else:
    print ("we're in the else")

we're in the 'if'

a = "False"
if a:
    print("we're in the 'if'")
else:
    print("we're in the 'else'")

we're in the 'if'

Tip

If you were surprised by that, think about the difference between the literal False and the string "False"

a = 5
b = 10
if a and b:
    print("a is", a)
    print("b is", b)

a is 5
b is 10

Lists

animals= ['dog', 'cat', 'panda']
if panda in animals:
    print("found it!")

---------------------------------------------------------------------------
NameError                                 Traceback (most recent call last)
/Users/glupyan/gitRepos/psych750.github.io/notebooks/review_of_fundamentals_a.ipynb Cell 30 in <cell line: 2>()
      <a href='vscode-notebook-cell:/Users/glupyan/gitRepos/psych750.github.io/notebooks/review_of_fundamentals_a.ipynb#X41sZmlsZQ%3D%3D?line=0'>1</a> animals= ['dog', 'cat', 'panda']
----> <a href='vscode-notebook-cell:/Users/glupyan/gitRepos/psych750.github.io/notebooks/review_of_fundamentals_a.ipynb#X41sZmlsZQ%3D%3D?line=1'>2</a> if panda in animals:
      <a href='vscode-notebook-cell:/Users/glupyan/gitRepos/psych750.github.io/notebooks/review_of_fundamentals_a.ipynb#X41sZmlsZQ%3D%3D?line=2'>3</a>     print("found it!")

NameError: name 'panda' is not defined

animals= ['dog', 'cat', 'panda']
if "panda" or "giraffe" in animals:
    print("found it!")

found it!

animals= ['dog', 'cat', 'panda']
if "panda" and "giraffe" in animals:
    print("found it!")

if ["dog", "cat"] in animals:
    print ("we're here")

some_nums = range(1,10)
print(list(some_nums))
print(some_nums[0])

[1, 2, 3, 4, 5, 6, 7, 8, 9]
1

animals= ['dog', 'cat', 'panda']
print(animals[-1])

panda

animals= ['dog', 'cat', 'panda']
print(animals.index('cat'))

1

animals= ['dog', 'cat', 'panda']
more_animals = animals+['giraffe']
print (more_animals)

['dog', 'cat', 'panda', 'giraffe']

animals= ['dog', 'cat', 'panda']
more_animals = animals.append('giraffe')
print (more_animals)

None

Note

The above is a tricky one! The issue is that append() does not return a value. It simply appends.

Compare the above with what happens in the code below

animals= ['dog', 'cat', 'panda']
animals.append("giraffe")
print(animals)

['dog', 'cat', 'panda', 'giraffe']

animals= ['dog', 'cat', 'panda']
for num,animal in enumerate(animals):
    print(f"Number {num+1} is {animals}")

Number 1 is ['dog', 'cat', 'panda']
Number 2 is ['dog', 'cat', 'panda']
Number 3 is ['dog', 'cat', 'panda']

animals= ['dog', 'cat', 'panda']
for num,animal in enumerate(animals):
    print(f"Number {num} is {animal}")
print(f"\nWe have {len(animals)} animals in our list.")

Number 0 is dog
Number 1 is cat
Number 2 is panda

We have 3 animals in our list.

animals= ['dog', 'cat', 'panda']
while animals:
    print (animals.pop())

print(f"\nWe have {len(animals)} animals in our list")

panda
cat
dog

We have 0 animals in our list