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Python2 is EOL; Python3 stores strings as unicode by default (not ascii).
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In Python, indentation is used to indicate code blocks.
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Backslashes "" can be used to interpret multiple lines as a single line.
- Variables & data types:
name = "neut"
name_length = 4
print(type(name))
#str
print(type(name_length))
#int
name_len = int("4")
print(type(name_len))
#int
name_list = ["a", "b", "c"]
name1, name2, name3 = name_list
print(name1, name2, name3)
#a b c
#there are other data types as well- Numbers:
t1_int = 1
t1_float = 1.0
t1_complex = 3.14j
t1_hex = 0xa
print(t1_hex)
#10
print(type(t1_hex))
#int
t1_octal = 0o10
print(t1_octal)
#8
print(type(t1_octal))
#int
print(1 + 0x1 + 0o1)
#3
#helper functions
print(abs(4), abs(-4))
#4 4
print(round(8.4), round(8.5), round(8.6))
#8 8 9
print(bin(8), hex(8))
#0b1000 0x8- Strings:
string1 = "A String!"
string2 = """multi-line
quote
!"""
#escaped characters
string3 = "I\"m an escaped character\nNewline"
string4 = "a" * 10
print(len(string4))
#10
#we can use inbuilt functions for strings
#functions can be chained as well
#string concatenation
print("String4 is " + str(len(string4)) + "characters long!")
#using format placeholder
print("String4 is {} characters long!".format(len(string4)))- Booleans & Operators:
not_valid = False
print(not_valid == True)
#False
print(not_valid != True)
#True
print(not not_valid)
#True
print((10 < 9) == True)
#False
print(10 < 9)
#False
print(bool(0))
#False
print(bool(1))
#True
x = 13
y = 5
print(bin(x))
#0b1101
print(bin(x)[2:].rjust(4,"0"))
#1101
#remove 0b from binary
#and ensure 4-digit output, with 0s to fill in
print(x & y)
#bitwise operator AND- Tuples:
#immutable
items = ("item1", "item2", "item3")
repeated = ("again",) * 4
mixed = ("A", 1, ("B", 0))
combined = items + repeated
#combine tuples
print("item2" in items)
#True
print(items.index("item3"))
#2
print(items[0])
#item1
#slicing
print(items[0:2])
#('item1', 'item2')- Lists:
#lists can be edited
list1 = ["A", "B", 1, 2.0, ["P"], [], list(), ("A")]
#can contain multiple types
print(list1[0])
#A
print(list1[4][0])
#P
list1[0] = "a"
print(list1)
#prints updated list
del list1[0]
#deletes first element
list1.insert(0, "A")
#inserts element at 0th index
list1.append("last")
#list has multiple inbuilt functions
#such as max, min, index, count, pop, extend
list2 = list1
#both lists point to same data
#if we make changes in list1, list2 will also change
#to only copy values
list3 = list1.copy()
list4 = ["1", "2", "3"]
list5 = list(map(float, list4))
#converts string to float- Dictionaries:
dict1 = {"a":1, "b":2, "c":3}
#key-value structure
print(len(dict1))
#3
print(dict1["a"])
#1
print(dict1.get("a"))
#1
print(dict1.keys())
#a,b,c
print(dict1.values())
#1,2,3
print(dict1.items())
#indices do not work in dictionaries
#duplicates not allowed in dicts
dict1["d"] = 4
print(dict1)
#modified
dict1["a"] = -1
#modified
dict1.update({"a":1})
#we can use pop() or del to remove pairs
dict1["c"] = {"a":1, "b":2}
#nested dictionaries
dict2 = {}
#empty dict- Sets:
#sets are unordered
#do not allow duplicates
set1 = {"a", "b", "c"}
print(set1)
#unordered output
set2 = {"a", "a", "a"}
print(set2)
#{'a'}
print(len(set2))
#1
set3 = set(("b", 1, False))
set1.add("d")
set3.update(set2)
list1 = ["a", "b", "c"]
set4 = {4, 5, 6}
set4.update(list1)
print(set4)
#contains 6 elements
#we can use union, intersection operations on sets
#we can use remove and discard on sets
#pop() removes arbitrary elements- Conditionals:
if True:
print("true")
#gets printed
if False:
print("false")
#does not get printed
if 1 < 1:
print("1 < 1")
elif 1 <= 1:
print("1 <= 1")
#only this gets printed
elif 2 <= 2:
print("2 <= 2")
else:
print("else code")
#comparisons can be combined using logical operators- Loops:
a = 1
while a < 5:
a += 1
print(a)
for i in [0,1,2,3,4]:
print(i+6)
#nested for loops
for i in range(3):
for j in range(3):
print(i,j)
for i in range(5):
if i == 2:
break
#ends loop
print(i)
for i in range(5):
if i == 2:
continue
#skip current iteration
print(i)
for c in "string":
print(c)
for k,v in {"a":1, "b":2, "c":3}.items():
print(k,v)- Reading & writing files:
f = open('top-100.txt')
print(f.read())
#prints file content
arrayOfLines = f.readlines()
print(f.readlines())
#empty array because pointer is at EOF
f.seek(0)
print(f.readlines())
#prints all lines array
f.seek(0)
for line in f:
print(line.strip())
f.close()
f = open("test.txt", "w")
#write mode
f.write("test line!")
f.close()
#"a" for append mode
#for larger files
with open('rockyou.txt', encoding='latin-1') as f:
for line in f:
pass- User input:
test = input()
print(test)
#prints input only after user enters some input
n = input("Enter a number:")
print(n)
while True:
test = input("Enter IP: ")
print(">>> {}".format(test))
if test == "exit":
break
else:
print("checking..")- Exceptions & error handling:
try:
f = open("doesnotexistfilename")
except:
print("File does not exist")
#prints custom error
try:
f = open("randomfile")
except FileNotFoundError:
print("File does not exist")
except Exception as e:
print(e)
#prints specific error
finally:
print("This always get printed")
n = 100
if n == 0:
raise Exception("n cannot be 0")
if type(n) is not int:
raise Exception("n must be an integer")
print(1/n)
#assertions
n = 1
assert(n != 0)
#triggers AssertionError if n is 0
print(1/n)- Comprehensions:
list1 = ['a', 'b', 'c']
#list comprehension
list2 = [x for x in list1]
list3 = [x for x in list1 if x == 'a']
list4 = [x for x in range(5)]
list5 = [hex(x) for x in range(5)]
list6 = [hex(x) if x > 0 else "X" for x in range(5)]
list7 = [x for x in range(5) if x == 0 or x == 1]
list8 = [[1,2,3],[4,5,6],[7,8,9]]
list9 = [y for x in list8 for y in x]
#[1,2,3,4,5,6,7,8,9]
set1 = {x + x for x in range(5)}
#{0,2,4,6,8}
list10 = [c for c in "stringtext"]
texthere = "".join(list10)- Functions & code reuse:
#define function
def function1():
print("function hello")
#call function
function1()
#returns a value
def function2():
return "hello!"
func2 = function2()
print(func2)
#accepts parameters
def function3(s):
print("\t{}".format(s))
function3("param")
def function4(s1, s2):
print("{} {}".format(s1,s2))
function4("check","this")
#default val
def function5(s1 = "default"):
print(s1)
#for any number of arguments
def function6(s1, *more):
print("{} {}".format(s1, " ".join([s for s in more])))
function6("func6", "arg1", "arg2", "arg3")
#dictionary of arguments
def function7(**ks):
for a in ks:
print(a, ks[a])
function7(a="1", b="2", c="3")
#global scope and function scope differ
v = 100
def function8():
#specify global scoped variable
global v
v += 1
print(v)
function8()
#101
print(v)
#101
#functions can call other functions
def function9():
function1()
#recursion
def function10(x):
print(x)
if x > 0:
function10(x-1)
function10(5)- Lambdas:
#single line anonymous function
add4 = lambda x : x + 4
print(add4(10))
add = lambda x, y : x + y
print(add(10,4))
print((lambda x, y : x * y)(2,3))
is_even = lambda x : x % 2 == 0
blocks = lambda x, y : [x[i:i+y] for i in range(0, len(x), y)]
print(blocks("string", 2))
#['st', 'ri', 'ng']
to_ord = lambda x : [ord(i) for i in x]
print(to_ord("ABCD"))