Use names to save information for later#

Jenny Palomino, Leah Wasser, Nathan Korinek, Elsa Culler

Modified Aug 30, 2023

Learn how to…

  • Explain how names are used in Python to store information.

  • Use Python code to give names to single data values including numbers and text strings.

  • Define computer memory and disk space

  • Describe what the workspace is in Python

  • Check the data type of a value in your workspace.

One of the features that makes computer programming such a powerful tool is the ability to retrieve data (i.e. information) you computed earlier from memory. In the analogy of your computer as a kitchen, your memory is the countertop space - you can access everything in it quickly, but it’s easy for it to get too crowded (and you don’t want to leave anything there when you’re done cooking!). Storing data in memory allows you to:

  • Hard code values into your code, like physical constants, conversion factors, and file locations

  • Perform multiple-step workflows without needing to save every intermediate step on your hard disk

You can store data (i.e. information) in Python by giving it a name. You will need to name everything that you want to re-use in your code (e.g. single numeric value, path to a directory or file). Without names for data, Python would only be able to perform the same calculations as a handheld calculator.

Get started with naming data in Python#

Why names and not variables?

You may also see named values referred to as variables in programming. We think this can be confusing, because most people are used to the word variable in the context of algebra, where a variable is a value that you don’t know the value of. In programming, the value of a variable is known, and doesn’t change unless you write over it. But if you prefer the term variable, other programmers will know what you mean!

A name in Python is used to save information that you want to re-use later in your code. You can think of it like the contacts in a cellphone – instead of remembering phone numbers, you save them under someone’s name so that you can use them again. Examples of things that you may wish to save in your code include:

  • numeric values

  • file names, paths, web addresses

  • or even larger objects such as a remote sensing image or a terrain model

Exercise 2

You can name a value in Python using the syntax name = value, replacing value and name with the information you wish to store, and the name you wish to give it:

Note

In order to see your results, you will have to call your variable (type out it’s name on the last line) at the end of the code cell.

Use the code cell below to practice naming some values. You can start by running the code below, which stores the value 5 under the name an_int. Then, try saving the value 6.3 under the name a_float:

an_int = 5
an_int

5

This syntax for creating names is the same whether you are assigning a numeric or text value to a name. For example, below you assign the name name a the value of 3 which is a number:

a = 3

Here is an example of assigning a text string value to the same name named a.

a = "a word"

Notice that strings (character values) use double quotes "" to indicate a text string value.

Data Tip:

Some programming languages require values to be explicitly assigned a data type before storing them in memory (or creating a variable). You do not need to worry about this when using Python! Python is known as a dynamically typed language, meaning that it does it guesses the type of data based on how you enter it. For example, if you enter 2, Python will assume that is an integer, while "2" would be a string and 2.0 would be a float.

Easy to Understand Names Make Your Code Easier to Read#

Just like you want to use expressive naming conventions (names that represent what is stored within the directory) for directories on your computer, you also want to use short, clear names for your names to make your code easier to read. To follow best practices for name names, avoid the following:

  • spaces in your name names

  • complicated wording

  • long name names

  • words that do not represent what the name contains (example: my_name vs precip_data)

When naming a name, you want to keep the name short but specific enough that someone reading your code can understand what it contains. It is good practice to use underscores (e.g. boulder_precip_in) to create multi-word name names that provide specifics regarding the name’s content. The underscore makes the name name easier to read and follows Python PEP 8 best practices for code readability.

Data Tip:

Read more about expressive name names and clean code in this earth data science lesson.

names Are Available In Your Coding Environment Once Defined#

A key characteristic of names is that once you create a name in your coding environment (that is to say you run the actual line of code that defines the name), it is available throughout your code. So for example, if you create a name at the top of a Jupyter Notebook, the value associated with that name will remain the same and can be reused in cells lower down in the notebook.

Data Tip:

You can overwrite an existing name if you create a new name with the same name. For example, if you assign a = 5 in one cell and then assign a = "dog" in the next cell, the final value of a will be "dog".

While there are occasions in which you might want to overwrite an existing name to assign a new value to it, you want to make sure that you give names both clear and distinct names to avoid accidentally overwriting name values.

# Here you assign the name name temperature the value 55 (a number)
temperature = 55

temperature

55

# Note that you can easily reassign a name name 
# to contain a new value (a string / word in this case)
temperature = "doctor"

temperature

'doctor'

About Data Types in Python#

Python data types are important to understand when coding. Below you will learn more about the different types of names that you can store including:

  • Numbers (integers and floats)

  • Strings (letters / characters and words)

Numeric names in Python#

In Python, you can create names to store numeric values such as integers (int) which represent whole numbers and floating point numbers which represent decimal values (float).

Data Tip: For more advanced math applications, you can also use names to work with complex numbers (see Python documentation for more details). {: .notice–success}

As described previously, you do not need to define which numeric type you want to use to create a name. For example, you can create a int name called boulder_precip_in, which contains the value for the average annual precipitation in inches (in) in Boulder, Colorado, rounded to the nearest integer.

# This is a comment line in `Python`
boulder_precip_integer = 20

# You can see the value of any name by calling the name name
boulder_precip_integer

20

You can use the type() function to figure out the type of data stored in a name.

# What is the type of data stored in boulder_precip_in
type(boulder_precip_integer)

int

If your data has decimal places associated with it, it will be stored in Python as a type: float.

boulder_precip_float = 20.23

boulder_precip_float

20.23

type(boulder_precip_float)

float

How to Store Text names: Strings in Python#

To create a name containing a text string (str), you use quotation marks ("") around the value. For example:

name_name = "text"

While in Python the single quote ('') and the double quote ("") are used interchangeably (see the official Python Docs for more examples), we suggest that you use double quotes "" to define strings (type == str) following PEP8 code style for Python best practices. Using quotes, you can create str names that contain a single word or many words, including punctuation. Below are some examples of creating a string.

city = "Boulder"

city

'Boulder'

city_state = "Boulder, CO"

city_state

'Boulder, CO'

city_description = "Boulder, CO is the home of the University of Colorado, Boulder campus."

city_description

'Boulder, CO is the home of the University of Colorado, Boulder campus.'

What Does Float() Do?

Run the code in the cell below. What does the float() function do to the value stored in the name named a?

# Run the code below - what does the float() function do? 
a = 75
b = float(a)
print(a, b)


# What data type is name b? (hint: use the type() function to find out)

75 75.0

# Answer to the above activity

b_type = type(b)

# Float turned the integer a into a float name and assigned it to b

Interactive Activity - Create Some names

It’s time for you to create some names of your own! Create the following:

  1. a name called precip_float that stores a float value.

  2. a name called precip_int that stores an integer value.

  3. a name called location that stores the string for the location: New York City.

For these names, use the average annual precipitation in New York City, which is 46.23 inches.

HINT: you can coerce a floating point value to an integer using the int() function. Use int() to convert your floating point value to an integer. The name name should be precip_int.

Try the code below to see how this works:

a = 75.643
b = int(a)
print(a, b)

# Assigning the names from above

precip_float = 46.23
precip_int = int(precip_float)
location = "New York City"

Check the type#

In the activities above, you used the type() function to determine what type of data are stored in a name.

type(name_name)

For example, you can check the type of boulder_precip_in after each time that a name is created with that same name to see that the type changes from int to float.

boulder_precip_in = 21

type(boulder_precip_in)

int

boulder_precip_in = 20.68

type(boulder_precip_in)

float

You can also check the type of the name named city, which is a string (str) regardless of how many words (or punctuation) it contains.

city = "Boulder"

type(city)

str

city = "Boulder, CO is the home of the University of Colorado, Boulder campus."

type(city)

str

Checking the type for a name can help you make sure that you understand what a name contains and how it can be used. For example, you can actually create a str name that contain numbers if you use the syntax for creating a str name (e.g. name_name = "value"). Notice below that city_precip is still a str, even though it contains a number.

city_precip = "20.68"

type(city_precip)

str

If you wanted to perform math on that name, it would not work the way you think it should.

# Multiply city_precip by 2
city_precip * 2

'20.6820.68'

Thus, the value itself is not important for determining whether the name is a numeric or string type - the syntax does this.

A good reminder that it is important to make sure that you are defining names with the appropriate syntax to distinguish between numeric and string types.

Challenge - Data Types & Math#

Run the following code which divides name a by name b (a/b).

a = 5
b = 3
c = a/b

Use the type() function to determine what type of value is stored in each name defined (a, b, and c).

a = 5
b = 3
c = a/b

type_a = type(a)
type_b = type(b)
type_c = type(c)