Python

Variables are memory references

The address of an object can be obtained by using the id() function. The id() function returns the address of the memory of it’s argument as base-10 integer.

Objectives

Obtaining the base-10 address using id()

We can use the function hex() to convert the base-10 number to base-16

name = "Stacy"
print(f'name = {name}')
print(f'address of the name in decimal {id(name)}')

name = "Stacy"

print(f'name = {name}')

print(f'address of the name in decimal {id(name)}')

name = Stacy
address of the name in decimal 140492014052656

1 2	name = Stacy address of the name in decimal 140492014052656

Obtaining the base-10 address using hex()

name = "Stacy"
print(f'name = {name}')
print(f'address of the name in decimal {id(name)}')
print(f'address of the name in hex {hex(id(name))}')

name = "Stacy"

print(f'name = {name}')

print(f'address of the name in decimal {id(name)}')

print(f'address of the name in hex {hex(id(name))}')

name = Stacy
address of the name in decimal 140492014052656
address of the name in hex 0x7fc6d8976530

name = Stacy

address of the name in decimal 140492014052656

address of the name in hex 0x7fc6d8976530

Strictly speaking, name is not “equal” to “Stacy”. Instead, we can say name is a reference to a String object containing the value Stacy, and it is located at the memory address 0x7fc6d8976530.

Naming variables in Python

Objectives

What is a variable?

Variables can be considered as a box. In Python, you can put anything inside that box, without specifying the size or type, which will be needed in languages such as C, C++ or Java. Note that Python is case-sensitive. Be careful about using letters in different cases.

age = 25 # integer
email = "suresh@somedomainname.com" # string
address = "112 main street" # string
gpa = 3.9 # float

age = 25 # integer

email = "suresh@somedomainname.com" # string

address = "112 main street" # string

gpa = 3.9 # float

Declaring and assigning variables

In programming terms, we say that we just declared a variable, email, and assigned it to the string, user@aol.com. To do so, we’ll follow the procedure below:

email_address = "user@aol.com"

1	email_address = "user@aol.com"

Note that if you introduce a new variable, (declare it), but do not also assign it in the same line, Python will raise an error.

>>> name
Traceback (most recent call last):
  File "&lt;stdin>", line 1, in &lt;module>
NameError: name 'name' is not defined
>>>

>>> name

Traceback (most recent call last):

File "<stdin>", line 1, in <module>

NameError: name 'name' is not defined

>>>

So that error tells us that name is not defined. We just fix this by declaring name and assigning the variable in the same line.

name = "John"

1	name = "John"

Declaring variables without assignment

We have seen that we can have data without assigning it to variables. Sometimes we wish to declare a variable without assigning it to data. In Python, that’s a little tricky to do. As we just saw with name, declaring variables without assignment throws an error. Thankfully, Python has a special type for us that represents nothing at all.

age = None

1	age = None

None is a data type in Python that represents nothing. So, if we do not know the type of a variable and want to have the data to the variable be assigned later, we can assign that variable to None.

Notice that age is now assigned, but it is assigned to date type None.

Naming variables in Python

June 2, 2020 by Suresh Melvin Sigera Leave a Comment

Objectives

What is a variable?

age = 25 # integer
email = "suresh@somedomainname.com" # string
address = "112 main street" # string
gpa = 3.9 # float

age = 25 # integer

email = "suresh@somedomainname.com" # string

address = "112 main street" # string

gpa = 3.9 # float

Declaring and assigning variables

In programming terms, we say that we just declared a variable, email, and assigned it to the string, user@aol.com. To do so, we’ll follow the procedure below:

email_address = "user@aol.com"

1	email_address = "user@aol.com"

Note that if you introduce a new variable, (declare it), but do not also assign it in the same line, Python will raise an error.

>>> name
Traceback (most recent call last):
  File "&lt;stdin>", line 1, in &lt;module>
NameError: name 'name' is not defined
>>>

>>> name

Traceback (most recent call last):

File "<stdin>", line 1, in <module>

NameError: name 'name' is not defined

>>>

So that error tells us that name is not defined. We just fix this by declaring name and assigning the variable in the same line.

name = "John"

1	name = "John"

Declaring variables without assignment

age = None

1	age = None

None is a data type in Python that represents nothing. So, if we do not know the type of a variable and want to have the data to the variable be assigned later, we can assign that variable to None.

Notice that age is now assigned, but it is assigned to date type None.

AWS EC2: Install Anaconda on Linux Instance

July 14, 2018 by Suresh Melvin Sigera Leave a Comment

Go to https://aws.amazon.com

From the top right-hand corner select My Account, and click on AWS Management Console, Here you can sign in or create a new AWS account.

Once signed successfully, it should take you to the AWS Management Console. Now select EC2 under the Compute.

This will bring you to the EC2 Dashboard. Now select Launch Instance.

Here I’m going select Ubuntu Server 16.04 LTS (HVM), SSD Volume Type – ami-ba602bc2 Now click Select

Now we need to choose an instance type. I have decided to stay with the free tire. So go ahead and click on the t2.micro and then select configure instance details

Since this server is an experimental server I’m going to stick the default settings. Now you should see add storage window, keep everything as it is and click on Review and Launch.

By now you should be at Step 7: Review Instance Launch window

Now go ahead and click on Launch. This should ask you to create a new key pair or use an existing key pair. Select create a new key pair from the drop-down. When you naming your key make sure there are no spaces. I have named my key pair as myUbuntu. Now click on download key pair. DO NOT LOSE THIS! Now click on Launch Instance.

Now click on the AWS logo on the top left corner, this should take you to the AWS console dashboard. From here click on the EC2 under Compute. Now you should see we have the newly created instance is up and running. Make sure to give a name, I have decided to name my instance and myUbuntu.

So far so good! Now we need to connect to the instance. Select your newly created instance and click Connect.

Brilliant! now locate your .PEM file and open a new terminal window, and type chmod 400 myUbuntu.pem this will make set the correct permissions for us to connect to the remote host.

Now we can SSH into our server ssh -i "myUbuntu.pem" ubuntu@ec2-34-219-167-95.us-west-2.compute.amazonaws.com