what is Python loop (while, for)

what is Python loop (while, for)

  2월 16, 2022    Eunhan's library

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Loop Statement in Python

• Keyword: for, while
• for need to set number range
• while need to set when stop the repeatation
• use for: when you know how many repeat needed
• use while: when you do not know how many repeat needed

for or while [range condition] :
[space]code you want to repeat

for statement Example

for i in range(10): 
    print("Hi") # Hi printed 10 times

temp=[A,B,C]
for i in range(len(temp)): 
    print(i) # 0 1 2 index printed

temp=[A,B,C]
for i in range(temp): 
    print(i) # A B C values in List printed

for i, j in enumerate(a):
    print(i, ":", j) # 0 : A 1 : B 2 : C index and value

numbers = [9, 7, 7]
letters = ["z", "x", "y"]
for pair in zip(numbers, letters):
    print(pair)
# (9, 'z') (7, 'x') (7, 'y') index and value Tuple

for i in range(5, 10):  # 5 ~ 9
    print(i) # 5 6 7 8 9

a = "balloon"
for i in a:
    print(i) # b a l l o   loop until i is "o"
    if i == "o":
        break

while Statement

i = 0
while i < 5:
    print(i) # 0 1 2 3 4 loop until i is bigger than 5
    i = i + 1

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what is Python condition (if)

what is Python condition (if)

  2월 15, 2022    Eunhan's library

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condition statement in Python

if Statement

• Keyword: if, elif, else
• if must there before use elif, else

if [condition] :
[space]code you want to run
elif [condition] :
[space]code you want to run
else :
[space]code you want to run

if Statement Example

a = 3
if a > 5:
    print("a is bigger than 5")
elif a > 0:
    print("a is bigger than 0 but smaller than 5")
else:
    print("a is negative")

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what is Python Set

what is Python Set

  2월 14, 2022    Eunhan's library

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Set in Python

Definition

• One of the data structure in python.
• Create set of data

declaration

• use { and } to declare

setA={1,3,4,"test"} # {1, 'test', 3, 4}
setB={2,4,"test",5,6} # {2, 'test', 4, 5, 6}

Characteristics

• No duplicated value
• Do not care about order
• set algebra(union, intersection, difference, symmetric difference)

Set Algebra

union

Keyword: "|", "union()"

union example

setA={1,3,4,"test"} # {1, 'test', 3, 4}
setB={2,4,"test",5,6} # {2, 'test', 4, 5, 6}


print(setA|setB)
print(setA.union(setB))
# {1, 2, 3, 4, 5, 6, 'test'}

intersection

Keyword: "&","intersection()"

intersection example

setA={1,3,4,"test"} # {1, 'test', 3, 4}
setB={2,4,"test",5,6} # {2, 'test', 4, 5, 6}

print(setA&setB)
print(setA.intersection(setB))
# {'test', 4}

difference of sets

Keyword: "-","difference()"

difference of sets example

setA={1,3,4,"test"} # {1, 'test', 3, 4}
setB={2,4,"test",5,6} # {2, 'test', 4, 5, 6}

print(setA-setB)
print(setA.difference(setB))
# {1, 3}

symmetric difference

Keyword: "^","symmetric_difference()"

symmetric difference example

setA={1,3,4,"test"} # {1, 'test', 3, 4}
setB={2,4,"test",5,6} # {2, 'test', 4, 5, 6}

print(setA^setB)
print(setA.symmetric_difference(setB))
# {1, 2, 3, 5, 6}

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what is Python Dictionary

what is Python Dictionary

  2월 13, 2022    Eunhan's library

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Dictionary in Python

Definition

• One of the data structure in python.
• has key and value binded. You can fine value when you know the key
• very slimier with hashmap

declaration

• use { and } to declare
• the value can be list
• the key can be int or string. But not list. (TypeError: unhashable type: 'list')

dictionary={"key1":"value1","key2":"value2","key3":"value3"}

how to use

1. indexing like List
2. get() method

difference between the indexing and get method

If key does not exist, the indexing will return error. But get method will return None.

# List처럼 인덱스를 넣기
print(dictionary["key1"]) # value1
print(dictionary["key2"]) # value2
print(dictionary["key3"]) # value3
# print(dictionary["key4"]) # KeyError: 'key4' means there is no key

# get() 메서드를 사용
print(dictionary.get("key1")) # value1
print(dictionary.get("key2")) # value2
print(dictionary.get("key3")) # value3
print(dictionary.get("key4")) # return None, it does not cause error

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what is Python Tuple

what is Python Tuple

  2월 12, 2022    Eunhan's library

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Tuple in Python

Definition

• One of the data structure in python.
• Almost same as List But Tuple is not editable.
• Object.

declaration

use "(" and ")" to declear.
But, if there is a element in Tuple, you need to add comma

tuple1=(1,)
tuple2=(1,2,3)
notTuple=(0) #wrong, this is int type. comma needed

index structure

same as List indexing

characteristic

Tuple is not editable.

slicing

Same as List.

[starting index : ending index-1 : condition index]

• [0:8:3] = select index 0 to 7 by adding 3
• [:8:] = select index 0 to 7 by adding 1
• [7::] = select index 7 to -1 by adding 1
• [::-1] = select index 0 to -1 by adding -1

a = (0, 1, 2, 3, 4, 5, 6, 7, 8, 9)
print(a[0:8:3])  # (0, 3, 6)
print(a[:8:])  # (0, 1, 2, 3, 4, 5, 6, 7)
print(a[7::])  # (7, 8, 9)
print(a[::-1])  # (9, 8, 7, 6, 5, 4, 3, 2, 1, 0)

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what is Python List

what is Python List

  2월 12, 2022    Eunhan's library

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List in Python

Definition

• One of the data structure in python.
• Almost same as array in other languages.
• Object.

declaration

temp=[]
temp=list()
temp=[5,9,44]

index structure

characteristic

List in List is possible. This is same as 2D array in other languages
String in python is same as List

slicing

[starting index : ending index-1 : condition index]

• [0:8:3] = select index 0 to 7 by adding 3
• [:8:] = select index 0 to 7 by adding 1
• [7::] = select index 7 to -1 by adding 1
• [::-1] = select index 0 to -1 by adding -1

a = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
print(a[0:8:3])  # [0, 3, 6]
print(a[:8:])  # [0, 1, 2, 3, 4, 5, 6, 7]
print(a[7::])  # [7, 8, 9]
print(a[::-1])  # [9, 8, 7, 6, 5, 4, 3, 2, 1, 0]

Arithmetic Operation

a=[1,2,3]
b=["apple","house","computer"]

print(a+b) # [1, 2, 3, 'apple', 'house', 'computer']
# print(a+3) # error
# print(a-b)  # error
# print(a-3) # error
# print(a*b) # error
print(b*3) # ['apple', 'house', 'computer', 'apple', 'house', 'computer', 'apple', 'house', 'computer']
print(b*0) # []
# print(a/b) # error
# print(a/3) # error

add element

• append() = add a new element behind
• extend() = add new elements behind
• insert() = add new elements by index
• [] = add new elements by index condition

a=[1,2,3,4,5,6,7,8,9]
b=["apple","house","computer"]


a.append("test")
print(a) #[1, 2, 3, 4, 5, 6, 7, 8, 9, 'test']
a=[1,2,3,4,5,6,7,8,9]
a.append(b)
print(a) #[1, 2, 3, 4, 5, 6, 7, 8, 9, ['apple', 'house', 'computer']]
a=[1,2,3,4,5,6,7,8,9]
a.extend("test")
print(a) #[1, 2, 3, 4, 5, 6, 7, 8, 9, 't', 'e', 's', 't']
a=[1,2,3,4,5,6,7,8,9]
a.extend(b)
print(a) #[1, 2, 3, 4, 5, 6, 7, 8, 9, 'apple', 'house', 'computer']
a=[1,2,3,4,5,6,7,8,9]
a.insert(2,"test")
print(a) #[1, 2, 'test', 3, 4, 5, 6, 7, 8, 9]
a=[1,2,3,4,5,6,7,8,9]
a.insert(2,b)
print(a) #[1, 2, ['apple', 'house', 'computer'], 3, 4, 5, 6, 7, 8, 9]
a=[1,2,3,4,5,6,7,8,9]
a[3:]=b
print(a) #[1, 2, 3, 'apple', 'house', 'computer']
a=[1,2,3,4,5,6,7,8,9]
a[:4]=b
print(a) #['apple', 'house', 'computer', 5, 6, 7, 8, 9]
a=[1,2,3,4,5,6,7,8,9]
a[6:6]=b
print(a) #[1, 2, 3, 4, 5, 6, 'apple', 'house', 'computer', 7, 8, 9]
a=[1,2,3,4,5,6,7,8,9]
a[6:7]=b
print(a) #[1, 2, 3, 4, 5, 6, 'apple', 'house', 'computer', 8, 9]

delete element

• remove() = delete by value
• del = delete by index or list
• pop() = index or last one

a=[1,2,3,4,5,6,7,8,9]
a.remove(1) # delete value 1
print(a) # [2, 3, 4, 5, 6, 7, 8, 9]
a=[1,2,3,4,5,6,7,8,9]
# a.remove(98) # error
# print(a)
a=[1,2,3,4,5,6,7,8,9]
del a[3] # delete index 3
print(a) # [1, 2, 3, 5, 6, 7, 8, 9]
a=[1,2,3,4,5,6,7,8,9]
del a[3:7] # delete index 3 to 6
print(a) # [1, 2, 3, 8, 9]
a=[1,2,3,4,5,6,7,8,9]
temp=a.pop() # return and delete the last element of the list
print(a) # [1, 2, 3, 4, 5, 6, 7, 8]
print(temp) # 9
a=[1,2,3,4,5,6,7,8,9]
temp=a.pop(1) # return and delete the index 1
print(a) # [1, 3, 4, 5, 6, 7, 8, 9]
print(temp) # 2

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what is Python Operaters(+-/*)

what is Python Operaters(+-/*)

  2월 11, 2022    Eunhan's library

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Arithmetic Operation in Python

Result tables

+, -, *, /, //, %, **, <, >, <=, >= table

When computer created and programming language started, 1 was true and 0 was false.

== table

unlike Java, this is not comparing class. it compare values.

and, or truth table

As above table, the "and" "or" are for true and false.
If you put other type, or gate return B value
If you put other type, and gate return A value

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what is Python Variables

what is Python Variables

  2월 11, 2022    Eunhan's library

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Python Variables

types

scalar and non-scalar
both object

scalar

• int : integer
• float : real number
• bool : True or False
• none : Null

non-scalar

• String : data values that are made up of ordered sequences of characters, such as "hello world"

checking data type

print(type(Variable))

Case-Sensitive

a and A are different variable

Casting

x = str(4)    # "4"
y = int(4)    # 4
z = float(4) # 4.0

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