Intro to CV and Python

3 == 5

72 >= 2

test_str = "test"
test_str == "test"  # can also compare strings

sum_ = 0

if sum_ == 0:
    print("sum_ is 0")
elif sum_ < 0:
    print("sum_ is less than 0")
else:
    print("sum_ is above 0 and its value is " + str(sum_))  # Cast sum_ into string type.

store_name = "Walmart"

if "Wal" in store_name:
    print("The store is not Walmart. It's " + store_name + ".")
else:
    print("The store is Walmart.")

for letter in store_name:
    print(letter)

a_range = range(5)
print(a_range)
print("range(5) gives" + str(list(range(5))))  # By default starts from 0
print("range(1,9) gives: " + str(list(range(1, 9))))  # From 1 to 8 (Again the end index is exclusive.)

for index in range(len(store_name)):  # length of a sequence
    print("The %ith letter in store_name is: %s" % (index, store_name[index]))

x = [i for i in range(10)]
print(x)

x = [i + 2 for i in range(10)]
print(x)

x = [i ** 2 for i in range(10) if i % 2 == 0]
print(x)

x = 2

while x < 10:
    print(x)
    x = x + 1

store_name = "Walmart"

index = 0
while True:
    print(store_name[index])
    index += 1  # a += b means a = a + b
    if store_name[index] == "a":
        print("End at a")
        break  # instead of setting flag to False, we can directly break out of the loop
        print("Hello!")  # This will NOT be run

for letter in store_name:
    if letter == "a":
        continue  # Not printing a
    else:
        print(letter)

def F(n):  # bonus- what does this function do?
    if n < 0:
        print("Incorrect input")
    elif n == 0:
        return 0
    elif n == 1:
        return 1
    else:
        return F(n - 1) + F(n - 2)

print(F(2))

print(F(3))

print(F(5))

print(F(7))

def geo_seq(a_1, q, n):
    a_n = a_1 * (q ** (n - 1))
    S_n = (a_1 * (q ** n - 1)) / (q - 1)
    return a_n, S_n

print(geo_seq(2, 2, 1))  # multiple outputs returns as a tuple

print(geo_seq(2, 2, 2))

print(geo_seq(2, 2, 2))

print(geo_seq(2, 2, 3)[1])  # get only second element

def geo_seq_optional_args(a_1, q=2, n=1):
    a_n = a_1 * (q ** (n - 1))
    S_n = (a_1 * (q ** n - 1)) / (q - 1)
    return a_n, S_n

print(geo_seq_optional_args(2))

print(geo_seq_optional_args(2, n=2))

class Employee:

    # the function that is being called each time a new instance is created
    def __init__(self, name="Jhon", salary=10000):
        # per instance variables
        self.name = name
        self.salary = salary

    def display_employee(self):
        print("Name : " + self.name + ", Salary: " + str(self.salary))

    def change_salary(self, new_salary):
        self.salary = new_salary

emp1 = Employee()  # create new instance
emp1.display_employee()

emp2 = Employee("Bob", salary=20000)  # create new instance
emp2.display_employee()

emp2.change_salary(30000)
emp2.display_employee()

# instance variables are also accessible - no such thing private/public vars
emp2.name = "Larry"
emp2.display_employee()

f = open("tmp1.csv", "w")  # f is a file handler, while "w" is the mode (w for write)
for item in range(6):
    f.write(str(item) + "\n")
f.close()  # close the filer handler for security reasons.

with open("tmp2.csv", "w") as f:
    for item in range(4):
        f.write(str(item))
        f.write("\n")
# no need to close file, when out of 'with' scope the file closes automatically

with open("tmp2.csv", "a") as f:  # 'a' == append to end of file
    for item in range(15, 19):
        f.write(str(item) + "\n")

f = open("tmp1.csv", "r")  # this time, use read mode
contents = [
    item.strip("\n") for item in f
]  # list comprehension. This is the same as for-loop but more concise + stripping newline
print(contents)
f.close()

with open("tmp2.csv", "r") as f:
    print(f.readlines())

# delete the files...
import os

os.remove("tmp1.csv")
os.remove("tmp2.csv")

import math  # use import to load a library

x = 3
print("e^x = e^3 = %f" % math.exp(x))
print("log(x) = log(3) = %f" % math.log(x))

from math import exp  # You can import a specific function

print(exp(x))  # This way, you don't need to use math.exp but just exp

from math import *  # Import all functions - not recommended do to overriding of functions

print(exp(x))
print(log(x))  # Before importing math, calling `exp` or `log` will raise errors

import math as m

m.exp(3)