David Dongmin Oh

Coding is life, Life is coding

3 minute read

This is a self note while taking the online course from:

LinkedIn Learning: Learning Python by Joe Marini

LinkedIn Learning: Python Essential Training by Bill Weinman

1. Variables

f = 1234 # global variable
def someFunction():
    f="def" # local variable
    print(f)

someFunction()
print(f)

Result:

def
1234

2. Functions

  • Basic function
def basic_func():
    print("This is basic function")
  • Function with arguments
def argument_func(arg1, arg2):
    print("This function takes", arg1, "and", arg2)
  • Function that returns a value
def cube(x):
    return x*x*x
  • Function with default values for an argument
def power(num, a=1): # a has a default value 1
    result = 1
    for i in range(a):
        result = result * num
    return result
  • Function with variable number of arguments
def multi_add(*args):
    result = 0
    for x in args:
        result = result + x
    return result

3. Conditional

  • can assign values with conditional statements
x = 10
y = 11
st = "x is less than y" if (x < y) else "x is greater than or the same as y"
print(st)

Result:

x is less than y
  • is, in kewords
# A is B
a = 1
b = 1
if a is b:
    print('a is b')
else:
    print('a is not b')

# a is in A
A = [1,2,3,4]
if 1 in A:
    print('1 is in A')
else:
    print('1 is not in A')

Result:

a is b
1 is in A

4. Loop

  • enumerate() function for each index and value in a collection
days = ['Mon', 'Tue', 'Wed', 'Thu', 'Fri', 'Sat', 'Sun']
for i, d in enumerate(days):
    print(i, d)

Result:

0 Mon
1 Tue
2 Wed
3 Thu
4 Fri
5 Sat
6 Sun

5. Numeric

  1. float type –> sacrificing accuracty for precision
  2. DO NOT USE FLOAT FOR ACCURACY ex) Money
  3. Numeric types (int, float, decimal) are immutable!
  • Problem with calculating float numbers
x = .1 + .1 + .1 - .3  # in a real world, this should be zero
print('x is {}'.format(x))  # not actually zero (almost zero)
print(type(x))

x is 5.551115123125783e-17
<class 'float'>
  • Use Decimal module for accurate calculation
from decimal import *

# use modules for accuracy
a = Decimal('.10')
b = Decimal('.30')
y = a + a + a - b
print('y is {}'.format(y))
print(type(y))

y is 0.00
<class 'decimal.Decimal'>

6. Sequence Type

  • List
x = [1, 2, 3, 4]  # list is created with [] brackets
x[0] = 0  # list is mutable
for i in x:
    print("i is {}".format(i))
print("list x is {}".format(x))
  • Tuple
y = (1, 2, 3, 4)  # tuple is created with () parentheses
for j in y:
    print("j is {}".format(j))
print("tuple y is {}".format(y))

y[0] = 0  # this line is an error -> tuple is immutable
  • range()
z = range(5)  # range function creates a sequence from 0 to n-1

for k in z:
    print("k is {}".format(k))

print("range(5, 30, 5) is {}".format(range(5, 30, 5)))

z[0] = 0 # this line is also an error -> range sequence is immutable
  • Accessing specific range of sequence
SSN = "12121515"

print("first four digit: " + SSN[:4])
print("last four digit: " + SSN[-4:])
print("except last two digit: " + SSN[:-2])

(Result)

first four digit: 1212
last four digit: 1515
except last two digit: 121215
  • Dictionary
# dictionary: searchable sequence with key value pairs
w = {'one': 1, 'two': 2, 'three': 3, 'four': 4}

# prints only keys
for l in w:
    print('l is {}'.format(l))

# prints out tuple of key and value
for k, v in w.items():
    print('k: {}, v: {}'.format(k, v))

# dictionary is mutable
w['one'] = 101
print('dictionary is mutable:')
print('k: one, v: {}'.format(w['one']))

(Result)

l is one
l is two
l is three
l is four
k: one, v: 1
k: two, v: 2
k: three, v: 3
k: four, v: 4
dictionary is mutable:
k: one, v: 101

7. Object

class Dog:
    sound = "Woof-Woof"
    walking = "Walks like a dog"

    # self = reference keyword for object
    def bark(self):
        print(self.sound)

    def walk(self):
        print(self.walking)


def main():
    moly = Dog()
    moly.bark()
    moly.walk()


if __name__ == "__main__":
    main()

(Result)

Woof-Woof
Walks like a dog

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