Basic Python

Variables

a = 1
b = "some string"
c = 'string as well '
b_c = 'some string'

Python is a dynamically typed language

a = 1
print(a)
print(type(a)) # use type() to see object type
a = "asd"
print(a)
print(type(a))
a = [1,2,3]
print(a)
print(type(a))

1
<class 'int'>
asd
<class 'str'>
[1, 2, 3]
<class 'list'>

if

if simmilar to C/C++:

if condition :
    code
elif condition : (optional)
    code
else: (optional)
    code 

***or***

if(condition):
    code
elif(condition): (optional)
    code
else: (optional)
    code 

one line if:

code if condition else code

comparsion operators:

== - equal
!= - unequal
<, >, >=, <= - so on

b = "string"
b_c = "string"

if(b == b_c):
    print("a equals b")
else:
    print("nope")


if b != "bit infra":
    print("super")

a equals b
super

logical operators:

and - conjunction (&& w C++)
or - disjunction (|| w C++)
*not - negation (! w C++)

a = 1
b = '1'

if a == 1 and b == '1':
    print("OK")
else:
    print("Nope")

OK

Loops

while

while condition:
    code

i = 1
while(True):
    print(i)
    i+=1

1
2
3
4

for

for loop that iterates through something e. g.:

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

1
2
3
4

in general:

 for variable in iterable_object:
    code

a = [(1,2,3), (3,4,5)]

for x,y,_ in a:
    print(x, y)

1 2
3 4

Collections

list - array
tuple - tuple
dict - dictionary (HashMap(java), unordered_map(C++))
set - set (HashSet(java), unordered_set(C++))

a = [4,5,6] # list(4,5,6)
a.append(1)
a.append(2)
a.insert(1,3)
print(a)

a[0] = 24
print(a)

print(len(a))
print(a.pop())
print(a)
print(a[0])

print(5 in a)

[4, 3, 5, 6, 1, 2]
[24, 3, 5, 6, 1, 2]
6
2
[24, 3, 5, 6, 1]
24
True

a = (1,2)
print(type(a))
#a[1] = 3 # typles are immutable throws TypeError
print(a[0])
print(5 in a)

a = list(a) #converte to list
print(a)
a[1] = 3
print(a)

<class 'tuple'>
1
False
[1, 2]
[1, 3]

a = set()
a.add('a')
a.add('b')
print(a)
a.add('a')
a.remove('a')
print(a)
# a.remove('a') # throws an KeyError
if('a' in a):
    a.remove('a')
else:
    print("there is no a")
print(len(a))

{'b', 'a'}
{'b'}
there is no a
1

a = dict()
a[(1,2)] = "para 1"
a[(4,5)] = "para 2"

keys = list(a.keys())

print(keys)
print(a.items())
print((1,2) in a)
print((1,3) in a)
print(a[(1,2)])
del a[(1,2)]
#print(a[(1,2)]) # throws an KeyError
print(keys)

[(1, 2), (4, 5)]
dict_items([((1, 2), 'para 1'), ((4, 5), 'para 2')])
True
False
para 1
[(1, 2), (4, 5)]

N-dimensional arrays

We use generators:
[ variable for iterator/'_' in iterable_object ]
e g.:

b = input()
a = [int(i) for i in b.split()]
print(a)
a = [[1,2]]*10
a[0][1] = 3
a

123
[123]

[[1, 3],
 [1, 3],
 [1, 3],
 [1, 3],
 [1, 3],
 [1, 3],
 [1, 3],
 [1, 3],
 [1, 3],
 [1, 3]]

Functions

def function_name(parameters divided by comma):
    code

def func(a,b,c):
    print(a)
    return b+c

r = func(1,2,3)
r

1

5

def func2(a):
    print(a*2 + 1)

r = func2(2)
print(r)

5
None

def funcZ(a):
    
    def funcW(b):
        return b*a
    
    return funcW

my_f = funcZ(4)
print(my_f.__name__)
my_f(5)

funcW

20

funcW(3)

---------------------------------------------------------------------------
NameError                                 Traceback (most recent call last)
<ipython-input-36-529d2743ae28> in <module>()
----> 1 funcW(3)

NameError: name 'funcW' is not defined

Importing libraries

import library_name

import numpy
a = numpy.array([1,2])
a

array([1, 2])

import library_name as alias

import numpy as np
a = np.array([1,2])
a

array([1, 2])

from library_name import function1, function2

from numpy import array, linspace
a = array([1,2])
print(linspace(1,5))
a

[1.         1.08163265 1.16326531 1.24489796 1.32653061 1.40816327
 1.48979592 1.57142857 1.65306122 1.73469388 1.81632653 1.89795918
 1.97959184 2.06122449 2.14285714 2.2244898  2.30612245 2.3877551
 2.46938776 2.55102041 2.63265306 2.71428571 2.79591837 2.87755102
 2.95918367 3.04081633 3.12244898 3.20408163 3.28571429 3.36734694
 3.44897959 3.53061224 3.6122449  3.69387755 3.7755102  3.85714286
 3.93877551 4.02040816 4.10204082 4.18367347 4.26530612 4.34693878
 4.42857143 4.51020408 4.59183673 4.67346939 4.75510204 4.83673469
 4.91836735 5.        ]

array([1, 2])

from library_name import function1 as alias, function2 as alias

from numpy import array as ar, linspace as ls
a = ar([1,2])
print(ls(1,5))
a

[1.         1.08163265 1.16326531 1.24489796 1.32653061 1.40816327
 1.48979592 1.57142857 1.65306122 1.73469388 1.81632653 1.89795918
 1.97959184 2.06122449 2.14285714 2.2244898  2.30612245 2.3877551
 2.46938776 2.55102041 2.63265306 2.71428571 2.79591837 2.87755102
 2.95918367 3.04081633 3.12244898 3.20408163 3.28571429 3.36734694
 3.44897959 3.53061224 3.6122449  3.69387755 3.7755102  3.85714286
 3.93877551 4.02040816 4.10204082 4.18367347 4.26530612 4.34693878
 4.42857143 4.51020408 4.59183673 4.67346939 4.75510204 4.83673469
 4.91836735 5.        ]

array([1, 2])

warning : can cause a mental diseases

from library_name import *

no examples for this s**t

a = [1, 2, 3]
b = a.copy()
b[1] = 50
a

[1, 2, 3]

Classes

class ClassName(object):
    
    def __init__(cokolwiek, a, b, c):
        cokolwiek.a = a
        cokolwiek.b = b
        cokolwiek.__c = c
    
    def class_method(self):
        return self.a+self.b
    
    def method2(self, a, b):
        self.a += a
        self.b += b
        return self.a + self.b
    
    def __add__(self, ob2):
        return self.a + ob2.a
    

class_object1 = ClassName(2,3, 4)
print(class_object1.__c)
class_object2 = class_object1
class_object3 = ClassName(2,3)

class_object1.class_method()

---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-60-7218ce05626f> in <module>()
      1 class_object1 = ClassName(2,3, 4)
----> 2 print(class_object1.__c)
      3 class_object2 = class_object1
      4 class_object3 = ClassName(2,3)
      5 

AttributeError: 'ClassName' object has no attribute '__c'

class_object1 + class_object3

4

class_object1.method2(1, 1)

7

print(class_object1.a, class_object1.b)

3 4

print(class_object2.a, class_object2.b)

3 4

print(class_object3.a, class_object3.b)

2 3

Print

print(1)
print("String")
print(1, "String", sep=':')
try: 
    print(1 + "String")
except:
    print("nope")

1
String
1:String
nope

much better

print ( f " { variable } " )

num = 1
string = "String"
print(f"{num} {string}")

1 String

with .format

print ( " { 0 } ... { 1 } ... { n }".format( list of arguments ) )

*len(list of arguments) = n

num = 1
string = "String"
print("{1} {0} {0}".format(num, string), sep=' ')
print("{1} {0} {0}".format(num, string))

print('%s is %f' % (string, num))

String 1 1
String 1 1
String is 1.000000

*args

a = 3
b = 4
a, b = b, a

a

4

b

3

a, *args, b = 1, 2, 3, 4, 5, 6

a

1

args

[2, 3, 4, 5]

b

6

def fun_arg(*arg):
    print("Item | index")
    for index, item in enumerate(arg):
        print(f"{item} | {index}")

fun_arg(5, 10 , 69)

Item | index
5 | 0
10 | 1
69 | 2

**kwargs

def fun(**kwargs):
    for key, value in kwargs.items():
        print(f"{key} = {value}")

fun(BIT="AI", JAVA="SCRIPT")

BIT = AI
JAVA = SCRIPT

Lambda

lambda variable : function

fun = (lambda x : x**2)

tab = [1,2,3]

[fun(x) for x in tab]

[1, 4, 9]

for i in map(fun, tab):
    print(i)

1
4
9

tab = [5,4,-612,7,5,8]

tab.sort(key=(lambda x : (x%10)))
tab

[4, 5, 5, 7, -612, 8]

s = "dima"
t = "filip"

sl = slice(0,3)
s[sl]

'dim'

a = [[12,3,5,5,234], [1,234,4]]

[[1, 234, 4]]