Python Keywords

True / False

Boolean literals

a = True
b = False

and / or / not

Logical operators

a = True
b = False
print(a and b)
print(a or b)
print(not b)

False
True
True

as

To create an alias

For example importing a module:

import math as calc

assert

It's used a condition to make sure a condition is always true. It is mainly used in tests or debugging purpose.

Following will run fine:

s = 'hello!'
assert (len(s) > 1)

Following will end in an error:

s = ''
assert (len(s) > 1)

........
assert (len(s) > 1)
AssertionError

for / break / continue

Creating /terminating / continuing loops

for x in range(3, 6):
    if x % 4 == 0:
        continue
    if x % 2 == 0:
        break
print(x)

5

class

To crate a class

class Person:
    name = 'joe'
p = Person()
print(p.name)

joe

def

To define a function

def multiply(x, y):
    print(x * y)
multiply(3, 5)

15

del

To delete an object

class Person:
    name = 'joe'
p = Person()
del p
print(p)

NameError: 
name 'p' is not defined

if /elif / else

To create conditional statement

x = 3
if x < 3:
    print("less than 3")
elif x > 3:
    print("more than 3")
else:
    print("exactly 3")

exactly 3

import / from

Importing module / Importing specific part of module

from math import pi

in

(a) To iterate a list
(b) To check if an element is contained by a list

(a) To iterate:

num = [10, 20]
for x in num:
    print(x)

10
20

(b) To check element is in the list:

num = [10, 20]
result = 10 in num
print(result)

True

is

To test if two variable are equal

x = 2
y = 3
result = x is y
print(result)

False

lambda

To create anonymous functions

a = lambda x: print(x)
a(5)

5

None

To define a null variable

a = None
print(a)

None

nonlocal

To declare a non-local variable which allows to change variables defined outside of the current scope

def num():
    x = 3
    def num2():
        nonlocal x
        x = 5
    num2()
    return x
print(num())

5

If we remove line nonlocal x then the output will be 3.

global

To declare a global variable

def run():
    global x
    x = 5
run()
print(x)

5

pass

To use as empty code where empty blocks are not allowed

def run():
    pass

raise

To raise an error

name = ''
if len(name) == 0:
    raise Exception("name cannot be empty")

Exception: name cannot be empty

return

To return or exit a function

def square(x):
    if x < 0:
        return
    return x * x
print(square(3))
print(square(-3))

9
None

while

To create a while loop

x = 3
while x > 0:
    print(x)
    x = x - 1

3
2
1

try / except / finally

To catch an error. finally block will always execute, even there's no error

x = 0
try:
    x = 5 / x
except ZeroDivisionError:
    print("error")
finally:
    print("end")

error
end

with

Simplifies the use of try... finally

with open('my-file', 'w') as file: 
    file.write('test') 

yield

To create a generator that can be iterated

def even():
    for x in range(3, 8):
        if x % 2 == 0:
            yield x
for i in even():
    print(i)

4
6