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Python

Run

python3 ./Python/test.pl.py

Data types

Type
Text Type str
Numeric Types int, float, complex
Sequence Types list, tuple, range
Mapping Type dict
Set Types set, frozenset
Boolean Type bool
Binary Types bytes, bytearray, memoryview
None Type NoneType

Variables

n, m = 0, "abc"
# none is null
n = 4
n = None  # reassign value

Input & output

print('Hello world!')
print("Hello world!")
print("""Hello world!""")
print("Program print 'Hello world!'")

# print
name = "User"
print("Hello,", name, ".")  # Hello, User .
print("Hello,", name, ".", sep="")  # Hello,User.
print(f"Hello, {name}.")  # Hello, User.

# adding zeroes
print(f"{123:0>9}")  # 000000123
print(f"{123:0<9}")  # 123000000
print(f"{123:0^9}")  # 000123000

# string operations
print("-" * 10)  # ----------

# string to int (see also float(), str())
n_1 = "1"
n_2 = "2"
print(n_1 + n_2)  # 12
n_1 = int(n_1)
n_2 = int(n_2)
print(n_1 + n_2)  # 3

# operations
print(f"{2 ** 0.5:.2f}")  # 1.41
print(10 // 3)  # 3 Floor division
print(10 % 3)  # 1 Modulus
last_digit = 1234 % 10  # 4
hour = 9
min = 5
print(f"{hour:02d}:{min:02d}")  # 09:05

Logical operators

# if-elif-else
yesterday_temp = int(input())
today_temp = int(input())
if today_temp > yesterday_temp:
    print("Today is warmer than yesterday.")
elif today_temp < yesterday_temp:
    print("Today is colder than yesterday.")
else:
    print("Today is the same temperature as yesterday.")

# or, and
first_letter = input()
last_letter = input()
if (first_letter == "а" or first_letter == "А") and (
        last_letter == "я" or last_letter == "Я"):
    print("Right")
else:
    print("Wrong")

# if in string contains string
text = input()
if "if" in text:
    print("Right")
else:
    print("Wrong")

# match
color = input()
match color:
    case 'red' | 'yellow':
        print('Stop.')
    case 'green':
        print('drive')
    case _:
        print('wrong value')

# short if
print("A") if a > b else print("B")

# not
a = True
print(not a)

String functions

  • len(str) - string length
# string immutable
s = "123"
print(s[1:2])

# valid numeric strings can be converted
print(int("100") + int("100"))  # 200

# and numbers can be converted to strings
print(str(100) + str(100))  # 100100

# ASCII value
print(ord("a"))  # 97

# combine with a delimiter
strings = ["1", "2", "3"]
print(",".join(strings))  # 1,2,3

Arithmetic functions

  • min("y", "c", "z") # 1
  • max(1, 2) # 2
  • abs(-10) # 10
  • 5 / 2 # 2.5
  • 5 // 2 # 2
  • 3 // -2 # -2 round down, so negative round to -2
  • int(3 / -2) # -1
  • 10 % 3 # 1
  • -10 % 3 # 2
  • math.fmod(-10, 3) # -1
  • math.floor(3 / 2) # 1
  • math.ceil(3 / 2) # 2
  • math.sqrt(4) # 2.0
  • math.pow(2, 3) # 8.0
  • float("inf") # max Int
  • float("-inf") # min Int

Loops

while

n = 0
while n < 5:
    print(n)
    n += 1

for

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

for i in range(2, 5):
    print(i)

for i in range(5, 1, -1):
    print(i)

arr = [1, 2, 3]
for i in range(len(arr)):
    print(arr[i])

for n in arr:
    print(n)

# index and value
for i, n in enumerate(arr):
    print(f"{i} {n}")

# loop through two arrays simultaneously
nums1 = [1, 2, 3]
nums2 = [3, 4, 5]

for n1, n2 in zip(nums1, nums2):
    print(f"{n1} {n2}")

Arrays

like list

arr = [1, 2, 3]
arr[-1]  # 3 last value
arr[-2]  # 2 last second value
arr.append(4)
arr.append(5)
arr.pop()
arr.insert(1, 7)
arr[0] = 0

arr[1] * 5  # init array of size 5
len(arr)

arr = [1, 2, 3, 4]
arr[1:3]  # [2, 3] sublist aka slicing
arr.reverse()
arr.sort()  # ascending order
arr.sort(reverse=True)  # descending order

arr = ["fff", "aa", "erere"]
arr.sort(key=lambda x: len(x))

arr = [i for i in range(5)]  # [0, 1, 2, 3, 4]
arr = [i + i for i in range(5)]  # [0, 2, 4, 6, 8]

# 2D List
arr = [[0] * 4 for i in range(4)]  # 2d array of length 4 filled 0

Unpacking

a, b, c = [1, 2, 4]

Deque

Queues (double ended queue)

from collections import deque

queue = deque()
queue.append(1)
queue.append(2)
print(queue)  # deque([1, 2])

queue.popleft()
print(queue)  # deque([2])

queue.appendleft(3)  # deque([3, 2])
queue.pop()  # deque([3])

HashSet

mySet = set()
mySet.add(1)
mySet.add(2)
mySet.add(2)
print(mySet)  # {1, 2}
print(len(mySet))  # 2
print(1 in mySet)  # True
mySet.remove(2)  # {1}
# list to set
pritn(set([1, 2, 3]))

mySet = {i in i in range(5)}

HashMap

aka dict

myMap = {}
myMap["alice"] = 88
myMap["bob"] = 77
print("alice" in myMap)
myMap.pop("alice")

myMap = {"alice": 80, "bob": 90}

myMap = {i: i * 3 for i in range(3)}

val = myMap["xx"]  # KeyError if key is absent
print(map.get("xx"))  # None
print(map.get("xx", "default"))  # Default value

# looping through map
for key in myMap:
    print(key, myMap[key])

for val in myMap.values():
    print(val)

for key, value in myMap.items():
    print(key, value)

if key in dic.keys()

list (array) can't be used as key in hashmap. A list can be converted to a tuple, which can be used as a dict key: e.g.

d = {tuple([1, 2, 3]): 'value'}

Tuples

like array but immutable

tup = (1, 2, 3)

can be used as key's for hash map/set !! list can't be used as keys

myMap = {(1, 2): 3}

mySet = set()
mySet.add((1, 2))
print((1, 2) in mySet)

DefaultDict

Return a new dictionary-like object. defaultdict is a subclass of the built-in dict class. Provides default value for missing key.

Using list as the default_factory, it is easy to group a sequence of key-value pairs into a dictionary of lists:

s = [('yellow', 1), ('blue', 2), ('yellow', 3), ('blue', 4), ('red', 1)]
d = defaultdict(list)
for k, v in s:
    d[k].append(v)

sorted(d.items())
# [('blue', [2, 4]), ('red', [1]), ('yellow', [1, 3])]

Setting the default_factory to int makes the defaultdict useful for counting (like a bag or multiset in other languages):

s = 'mississippi'
d = defaultdict(int)
for k in s:
    d[k] += 1

sorted(d.items())
# [('i', 4), ('m', 1), ('p', 2), ('s', 4)]

Heap

under the hood are arrays

import heapq

minHeap = []
heapq.heappush(minHeap, 3)
heapq.heappush(minHeap, 2)
heapq.heappush(minHeap, 4)

print(minHeap[0])  # 2 - min value

while len(minHeap):
    print(heapq.heappop(minHeap))

no max heap by default, work around is to use min heap and multiply by -1 when push and pop

maxHeap = []
heapq.heappush(maxHeap, -1 * 3)
heapq.heappush(maxHeap, -1 * 2)
heapq.heappush(maxHeap, -1 * 4)

print(-1 * maxHeap[0])  # 2 - min value

while len(maxHeap):
    print(-1 * heapq.heappop(maxHeap))

arr = [2, 1, 3, 4]
heapq.heapify(arr)

while arr:
    print(heapq.heappop(arr))

Functions

def myFunc(m, n):
    return m * n


print(myFunc(2, 3))

Nested functions have access to outer variables

def outer(a, b):
    c = "c"

    def inner():
        return a + b + c

    return inner()


print(outer("a", "b"))

Can modify objects but not to reassign unless using nonlocal word

def double(val):
    val = val * 2


val = 5
double(val)
print(val)

Class

class MyClass:
    # Constructor
    def __init__(self, nums):
        # Create member variables
        self.nums = nums
        self.size = len(nums)

    def getLength(self):
        return self.size

Csv to Sql

# https://konbert.com/convert/excel/to/csv
import uuid;

f = open("data.csv", "r")
fr = open("result.sql", "w", encoding="utf-8")
for str in f:
    stringData = str.split(';')
    stringData = ["'{0}'".format(element) for element in stringData]
    stringData = [element.replace('\n', '') for element in stringData]
    formattedString = ", ".join(stringData)
    formattedString.replace('\n', ' ').replace('\r', '')

    fr.write(f"('{uuid.uuid4()}', {formattedString}),\n")

f.close()