Lecture Week 1 Fri 10/4

a = [1,2, 3]
b = a
b[0] = True

a

[True, 2, 3]

a = [1, 2, 3]

b = []
for elem in a:
    b.append(elem)

# what is b
b

[1, 2, 3]

b[0] = 0

b

[0, 2, 3]

a

[1, 2, 3]

d = {'a': 1, 3: False}

d['a']

1

d[3]

False

d[2] = 100

d

{'a': 1, 3: False, 2: 100}

c = d

c[2] = 99

c

{'a': 1, 3: False, 2: 99}

d

{'a': 1, 3: False, 2: 99}

a = [1, 2, 3]
b = [elem for elem in a]

a[0] = 100

a

[100, 2, 3]

b

[1, 2, 3]

def f(x):
    a = 1
    y = x + a
    return y

y = 1
b = f(1)
# what is y

y

1

a = 2

def myadd(x):
    b = x + a
    return b

a = 3
z = myadd(1)
# what is z
# myadd will use the a at the time of the call, not the time of the definition
# In other words, in a notebook enveironment, it depends on the order of execution the code, not the order of writing the code
z

4

def myfun(x):
    return x**2, x**3

a,b = myfun(2)
print(a)
print(b)

4
8

def gen_list(x, y = 1):
    return [x,y]

print(gen_list(1,2))

[1, 2]

print(gen_list(1))

[1, 1]

f1 = lambda x: x + 1

def f2(x):
    return x + 1

f1(1)

2

a = 2
f_add_a = lambda x: x + a
a = 3
f_add_a(1)

4

def myfun(n):
    if n == 1:
        return 1
    else:
        return n*myfun(n-1)

# how to sort by decreasing order of the absolute value of the elements
c = [5, -2, 3, -1, 4]

sorted(c, reverse=True, key = lambda x:abs(x))

[5, 4, 3, -2, -1]

c_abs = [1 if elem > 0 else -1 for elem in c]
c_abs

[1, -1, 1, -1, 1]