For Loops

5 main for loops is python

1) Regular loop

for i in range(5):
    print(i)

0
1
2
3
4

for i in range (8):
    print(i ** 2)

0
1
4
9
16
25
36
49

list = []
for i in range(8):
    list.append(i**2)
print(list)

[0, 1, 4, 9, 16, 25, 36, 49]

2) List loop

list = [2, 4, 6, 8]
for i in list:
    print(i)

2
4
6
8

3) Enumeration loop

list = [2, 4, 6, 8]
for i in enumerate(list):
    print("(Index, Elements) = {}".format(i))

(Index, Elements) = (0, 2)
(Index, Elements) = (1, 4)
(Index, Elements) = (2, 6)
(Index, Elements) = (3, 8)

list = [2, 4, 6, 8]
for i, j in enumerate(list):
    print("Index {} contains {}".format(i, j))

Index 0 contains 2
Index 1 contains 4
Index 2 contains 6
Index 3 contains 8

4) List Comprehension loop

list = [i ** 2 for i in range(8)]
print(list)

[0, 1, 4, 9, 16, 25, 36, 49]

5) Double for loop

for i in range(4):
    for j in range(4):
        print("i={}, j={}".format(i,j))

i=0, j=0
i=0, j=1
i=0, j=2
i=0, j=3
i=1, j=0
i=1, j=1
i=1, j=2
i=1, j=3
i=2, j=0
i=2, j=1
i=2, j=2
i=2, j=3
i=3, j=0
i=3, j=1
i=3, j=2
i=3, j=3

Booleans and if statments

a = True
b = False

print (a)

True

print(b)

False

c = a + b
print (c)

1

c = a - b
print(c)

1

a1 = False
b1 = False
c1 = a1 + b1
print (c1)

0

a1 = False
b1 = False
c1 = a1 - b1
print (c1)

0

print (a or b)

True

print (a and b)

False

print(not(b))

True

print (a and not(b))

True

if a:
    print("yes")

yes

if b:
    print("yes")

if not(b):
    print("yes")

yes

if a or b:
    print("yes")

yes

i = 0

a = i == 1

print(a)

False

a = i != 1

print(a)

True

if i == 0:
    print("yes")

yes

if i != 1:
    print("yes")

yes

i = 1
j = 0

if i != 1 or j == 0:
    print("yes")

yes

"bo" in "book"

True

if "bo" in "book":
    print("yes")

yes

if "be" in "book":
    print("yes")

if "be" in "book":
    print("yes")
else:
    print("no")

no

if "bo" in "book" and 1 == 2:
    print("yes")
elif "bo" in "book":
    print("only one is true")
else:
    print("no")

only one is true

if 0:
    print("yes")

if 1:
    print("yes")

yes

if 2:
    print("yes")

yes

if 5.4:
    print("yes")

yes

Nested if

age = int(input("Please enter your age: "))
gender = input("Please, enter your gender: ")

if age < 18:
    if gender == 'M' or gender ==  'm':
        print('son')
    else:
        print('daughter')
elif age >= 18 and age < 65:
    if gender == 'M' or gender ==  'm':
        print('father')
    else:
        print('mother')
else:
    if gender == 'M' or gender ==  'm':
        print('grandfather')
    else:
        print('grandmother')

Please enter your age: 4
Please, enter your gender: M
son

Problems

Problem 1

The equation for the height of a thrown ball is $y = -1/2 g t^2 + v_0 t$ where

• $t$ is time
• $y$ is the height of the ball
• $v_0$ is the initial upward speed of the ball
• $g$ is gravity ## دو توپ با سرعتهای متفاوت به سمت بالا پرتاب می شوند. ارتفاعهای آنها را بر حسب زمان رسم کنید

import numpy as np

t = np.linspace(0, 2, 100)
g = 9.8
v0_1 = 10
v0_2 = 15

print(t)

[0.         0.02020202 0.04040404 0.06060606 0.08080808 0.1010101
 0.12121212 0.14141414 0.16161616 0.18181818 0.2020202  0.22222222
 0.24242424 0.26262626 0.28282828 0.3030303  0.32323232 0.34343434
 0.36363636 0.38383838 0.4040404  0.42424242 0.44444444 0.46464646
 0.48484848 0.50505051 0.52525253 0.54545455 0.56565657 0.58585859
 0.60606061 0.62626263 0.64646465 0.66666667 0.68686869 0.70707071
 0.72727273 0.74747475 0.76767677 0.78787879 0.80808081 0.82828283
 0.84848485 0.86868687 0.88888889 0.90909091 0.92929293 0.94949495
 0.96969697 0.98989899 1.01010101 1.03030303 1.05050505 1.07070707
 1.09090909 1.11111111 1.13131313 1.15151515 1.17171717 1.19191919
 1.21212121 1.23232323 1.25252525 1.27272727 1.29292929 1.31313131
 1.33333333 1.35353535 1.37373737 1.39393939 1.41414141 1.43434343
 1.45454545 1.47474747 1.49494949 1.51515152 1.53535354 1.55555556
 1.57575758 1.5959596  1.61616162 1.63636364 1.65656566 1.67676768
 1.6969697  1.71717172 1.73737374 1.75757576 1.77777778 1.7979798
 1.81818182 1.83838384 1.85858586 1.87878788 1.8989899  1.91919192
 1.93939394 1.95959596 1.97979798 2.        ]

y_1 = -1/2 * g * t ** 2 + v0_1 * t
y_2 = -1/2 * g * t ** 2 + v0_2 * t

import matplotlib.pyplot as plt
plt.plot(t, y_1)

[<matplotlib.lines.Line2D at 0x7ff28c4fceb0>]

import matplotlib.pyplot as plt
plt.plot(t, y_2)

[<matplotlib.lines.Line2D at 0x7ff28ee0d580>]

import matplotlib.pyplot as plt
plt.plot(t, y_1)
plt.plot(t, y_2)

[<matplotlib.lines.Line2D at 0x7ff28ede8d30>]

import matplotlib.pyplot as plt
plt.plot(t, y_1)
plt.plot(t, y_2)
plt.xlabel("Time")
plt.ylabel("Height")

Text(0, 0.5, 'Height')

import matplotlib.pyplot as plt
plt.plot(t, y_1)
plt.plot(t, y_2)
plt.xlabel("Time")
plt.ylabel("Height")
plt.grid()

import matplotlib.pyplot as plt
plt.plot(t, y_1, label = "Ball Number 1")
plt.plot(t, y_2, label = "Ball Number 2")
plt.xlabel("Time")
plt.ylabel("Height")
plt.grid()
plt.legend()

<matplotlib.legend.Legend at 0x7ff28ff72e50>

Problem 2

statments = ["Quantum mechanics is a fundamental theory in physics that provides",
        "a description of the physical properties of nature at the scale of atoms and subatomic particles.",
        "It is the foundation of all quantum physics including quantum chemistry,"
        "quantum field theory,",
        "quantum technology,"
        "and quantum information science.",
        "Classical physics, the collection of theories that existed before the advent of quantum mechanics,"
        "describes many aspects of nature at an ordinary (macroscopic) scale,"
        "but is not sufficient for describing them at small (atomic and subatomic) scales."
        "Most theories in classical physics can be derived from quantum mechanics",
        "as an approximation valid at large (macroscopic) scale."]

statments

['Quantum mechanics is a fundamental theory in physics that provides',
 'a description of the physical properties of nature at the scale of atoms and subatomic particles.',
 'It is the foundation of all quantum physics including quantum chemistry,quantum field theory,',
 'quantum technology,and quantum information science.',
 'Classical physics, the collection of theories that existed before the advent of quantum mechanics,describes many aspects of nature at an ordinary (macroscopic) scale,but is not sufficient for describing them at small (atomic and subatomic) scales.Most theories in classical physics can be derived from quantum mechanics',
 'as an approximation valid at large (macroscopic) scale.']

statments[0]

'Quantum mechanics is a fundamental theory in physics that provides'

statments[1]

'a description of the physical properties of nature at the scale of atoms and subatomic particles.'

for i, line in enumerate(statments):
    if "quantum" in line:
        print("line {} contains quantum".format(i))

line 2 contains quantum
line 3 contains quantum
line 4 contains quantum

for i, line in enumerate(statments):
    if "Quantum" in line:
        print("line {} contains Quantum".format(i))

line 0 contains Quantum

for i, line in enumerate(statments):
    if "physics" in line:
        print("line {} contains physics".format(i))

line 0 contains physics
line 2 contains physics
line 4 contains physics

Problem 3

Sum numbers from 1 to 1000, except for those that can be divided by 3, and those that can be divided by 7

s = 0
for i in range(1001):
    if not(i % 3 == 0) and not(i % 7 == 0):
        s = s + i
print(s)

286284

s = 0
for i in range(101):
#     if not(i % 4 == 0) and not(i % 6 == 0):
        s = s + i
print(s)

5050

Python While Loops

i = 1
while i < 6:
  print(i)
  i += 1

1
2
3
4
5

i = 1
while i < 6:
  print(i)
  if i == 3:
    break
  i += 1 

1
2
3

i = 0
while i < 6:
  i += 1
  if i == 3:
    continue
  print(i)

1
2
4
5
6

i = 1
while i < 6:
  print(i)
  i += 1
else:
  print("i is no longer less than 6")

1
2
3
4
5
i is no longer less than 6

# Program to add natural
# numbers up to 
# sum = 1+2+3+...+n

# To take input from the user,
# n = int(input("Enter n: "))

n = 10

# initialize sum and counter
sum = 0
i = 1

while i <= n:
    sum = sum + i
    i = i+1    # update counter

# print the sum
print("The sum is", sum)

The sum is 55

'''Example to illustrate
the use of else statement
with the while loop'''

counter = 0

while counter < 3:
    print("Inside loop")
    counter = counter + 1
else:
    print("Inside else")

Inside loop
Inside loop
Inside loop
Inside else

a = ['Car', 'Book', 'Cat']
while a:
    print(a.pop(-1))

Cat
Book
Car

n = 5

while n > 0:

    n -= 1

    if n == 2:

        break

    print(n)

print('Loop ended.')

4
3
Loop ended.

n = 5

while n > 0:

    n -= 1

    if n == 2:

        continue

    print(n)

print('Loop ended.')

4
3
1
0
Loop ended.

n = 5
while n > 0:
    n -= 1
    print(n)
else:
    print('Loop done.')

4
3
2
1
0
Loop done.

a = ['car', 'cat', 'carpet', 'book']
s = 'shark'
i = 0
while i < len(a):
    if a[i] == s:
        print(s, 'found in list.')
        break
    i += 1
else:
    # Processing for item not found
    print(s, 'not found in list.')

shark not found in list.

a = ['car', 'cat', 'carpet', 'book']
s = 'cat'
i = 0
while i < len(a):
    if a[i] == s:
        print(s, 'found in list.')
        break
    i += 1
else:
    # Processing for item not found
    print(s, 'not found in list.')

cat found in list.

s = 'shark'
if s in a:
    print(s, 'found in list.')
else:
    print(s, 'not found in list.')

shark not found in list.

s = 'cat'
if s in a:
    print(s, 'found in list.')
else:
    print(s, 'not found in list.')

cat found in list.

try:
    print(a.index('shark'))
except ValueError:
    print(s, 'not found in list.')

shark not found in list.

try:
    print(a.index('cat'))
except ValueError:
    print(s, 'not found in list.')

1

while True:
    print('foo')

a = ['car', 'cat', 'carpet', 'book']
while True:
    if not a:
        break
    print(a.pop(-1))

book
carpet
cat
car

a

['car', 'cat', 'carpet', 'book']

a.pop(-1)

'book'

a

['car', 'cat', 'carpet']

a.pop(-1)

'carpet'

a

['car', 'cat']

a.pop(-1)

'cat'

a

['car']

a.pop(-1)

'car'

a

[]

Nested while Loops

a = ['car', 'cat']
while len(a):
    print(a.pop(0))
    b = ['carpet', 'book']
    while len(b):
            print('>', b.pop(0))

car
> carpet
> book
cat
> carpet
> book

a = ['car', 'cat']
a

['car', 'cat']

len(a)

2

a.pop(0)

'car'

a

['cat']

len(a)

1

a.pop(0)

'cat'

a

[]

len(a)

0

# One-Line while Loops
n = 5
while n > 0: n -= 1; print(n)

4
3
2
1
0

# One-Line if
if True: print('foo')

foo

# But you can’t do this:
while n > 0: n -= 1; if True: print('foo')

  File "/var/folders/dw/p9lncvq57tv4px69pk911vl40000gn/T/ipykernel_2914/4240503912.py", line 2
    while n > 0: n -= 1; if True: print('foo')
                         ^
SyntaxError: invalid syntax

Functions

def func1(x, y, z):
    return x ** 3 + y ** 2 + z 

Positional arguments of the function:

func1(1, 2, 3)

8

func1(2, 1, 3)

12

func1(3, 2, 1)

32

Keyword arguments of the function:

func1(x = 1, y = 2, z = 3)

8

func1(y = 2, x = 1, z = 3)

8

func1(z = 3, y = 2, x = 1)

8

Returning multiple values as a tuple

def func2(x,y,z, w):
    return (y + z + w) / x, (x + z + w) / y, (x + y + w) / z, (x + y + z) / w

x1, y1, z1, w1 = func2(2, 4, 6, 8)
print(x1, y1, z1, w1)

9.0 4.0 2.3333333333333335 1.5

def func2(x,y,z, w):
    return (y + z + w) / x, (x + z + w) / y, (x + y + w) / z, (x + y + z) / w

Values = func2(2, 4, 6, 8)
print(Values)

(9.0, 4.0, 2.3333333333333335, 1.5)

print (type(x1))

<class 'float'>

print(type(Values))

<class 'tuple'>

Anonymous (Lambda) Functions

def func3(x):
    return x + 10

print (func3(2))

12

func4 = lambda x: x + 10
print(func4(2))

12

x = lambda a, b : a * b
print(x(5, 6))

30

x = lambda a, b, c : a + b + c
print(x(5, 6, 2))

13

Why Use Lambda Functions?

The power of lambda is better shown when you use them as an anonymous function inside another function.

def myfunc(n):
  return lambda a : a * n

def myfunc(n):
  return lambda a : a * n

mydoubler = myfunc(2)

print(mydoubler(11)) 

22

def myfunc(n):
  return lambda a : a * n

mydoubler = myfunc(2)
mytripler = myfunc(3)

print(mydoubler(11))
print(mytripler(11))

22
33

def derivative(f, x, delta = 0.01): #returns derivative of f at value x
    return (f(x + delta) - f(x))/delta

def x_cube(x):
    return x ** 3

derivative(x_cube, 2)

12.060099999999707

def derivative(f, x, delta = 0.01): #returns derivative of f at value x
    return (f(x+delta) - f(x))/delta

derivative(lambda x: x ** 3, 2)

12.060099999999707

Multiple valued lambda function

func5 = lambda x, y, z, w : ((y + z + w) / x, (x + z + w) / y, (x + y + w) / z, (x + y + z) / w)

x1, y1, z1, w1 = func5(2, 4, 6, 8)
print(x1, y1, z1, w1)

9.0 4.0 2.3333333333333335 1.5

func5 = lambda x, y, z, w : ((y + z + w) / x, (x + z + w) / y, (x + y + w) / z, (x + y + z) / w)

Values = func5(2, 4, 6, 8)
print(Values)

(9.0, 4.0, 2.3333333333333335, 1.5)

Partial Argument Application of Lambda Function

def subtract(x, y):
    return x - y

subtract_10 = lambda x: subtract(x, 10)
print(subtract_10(6))

-4

iter function

# list of students
list1 = ['s', 't', 'u', 'd', 'e', 'n', 't', 's']
list1_iter = iter(list1)

print(next(list1_iter))    # 's'
print(next(list1_iter))    # 't'
print(next(list1_iter))    # 'u'
print(next(list1_iter))    # 'd'
print(next(list1_iter))    # 'e'
print(next(list1_iter))    # 'n'
print(next(list1_iter))    # 't'
print(next(list1_iter))    # 's'

s
t
u
d
e
n
t
s

dic1 = {'a':1, 'b':2, 'c':3}
for item in dic1:
    print(item)

a
b
c

dic1 = {'a':1, 'b':2, 'c':3}
dic1_iter = iter(dic1)

print(next(dic1_iter))
print(next(dic1_iter))
print(next(dic1_iter))

a
b
c

# ends the output with a <space> 
print("Amir" , end = ' ') 
print("Akbari")

Amir Akbari

# ends the output with a <@> 
print("Amir" , end = '@') 
print("gmail.com")

Amir@gmail.com

s = 0
f = (x ** 2 for x in range(10))
for x in f:
    print(x, end= ' ')
    s = s + x
print(f"===> sum = {s}")

print("sum obtained from sum function is also", sum(x**2 for x in range(10)))

0 1 4 9 16 25 36 49 64 81 ===> sum = 285
sum obtained from sum function is also 285

Generators

A generator is a concise way to contruct an iterable object. Normal functions execute and return a single object (this can be a list or tuple that contains multiple things). Generators return a sequence of values, but lazily; they pause at each one untill the next one is requested. This can save computation space. To create a generator, use the "yield" keyword.

def f(n = 10):
    for i in range(1, n + 1):
        yield i + 5

gen1 = f()
gen1

<generator object f at 0x7ff28ff11b30>

for x in gen1:
    print(x, end= ' ')

6 7 8 9 10 11 12 13 14 15 

def sentence_gen():
    yield 'Physics is the natural science '
    yield 'that studies matter, its fundamental constituents, '
    yield 'its motion and behavior through space and time, '
    yield 'and the related entities of energy and force.'

gen2 = sentence_gen()

for x in gen2:
    print(x, end='')

Physics is the natural science that studies matter, its fundamental constituents, its motion and behavior through space and time, and the related entities of energy and force.

Generator Expressions

Like lambda functions for functions, there are more concise way to make generators as well. This involves using a generator expression like such:

gen3 = (x ** 2 for x in range(11))
gen3

<generator object <genexpr> at 0x7ff29010bc10>

for x in gen3:
    print(x, end=' ')

0 1 4 9 16 25 36 49 64 81 100 

itertools module

Python’s Itertool is a module that provides various functions that work on iterators to produce complex iterators.

import itertools
   
# for in loop
for i in itertools.count(0, 5):
    if i == 35:
        break
    else:
        print(i, end =" ")

0 5 10 15 20 25 30 

import itertools
   
count = 0
   
for i in itertools.cycle('ABC'):
    if count > 7:
        break
    else:
        print(i, end = " ")
        count += 1

A B C A B C A B 

l = ['Course', 'Presented', 'For', 'Students']
count = 0
   
for i in itertools.cycle(l):
    if count > 10:
        break
    else:
        print(i, end = " ")
        count += 1

Course Presented For Students Course Presented For Students Course Presented For 

l = ['Course', 'Presented', 'For', 'Students']
   
# defining iterator
iterators = itertools.cycle(l)
   
for i in range(11):
    print(next(iterators), end = " ")

Course Presented For Students Course Presented For Students Course Presented For