Variables

Robot Framework variables are useful when:

• strings change often in the tasks. With variables you only need to make these changes in one place.
• creating system-independent tasks (${RESOURCES} instead of c:\resources, ${HOST} instead of 10.0.0.1:8080). Variables can be overwritten using command-line switches (--variable HOST:10.0.0.2:1234 --variable RESOURCES:/opt/resources) or environment variables.
• there is a need to have objects as arguments for keywords.
• different keywords need to communicate. Assign a return value from one keyword to a variable and pass it as an argument to another.
• values in the task data are long or complicated (${URL} is clearer than http://long.domain.name:8080/path/to/service?foo=1&bar=2&zap=42).

Readability and flexibility

Read more about using environment variables with Robocorp.

Different types of variables

Variable name consists of the type identifier ($, @, &, %), curly braces ({, }) and the variable name between the braces. Use capital letters with global variables in the *** Variables *** section (${SEARCH_URL}). Use small letters with local variables that are only available in certain tasks or user keywords (${search_url}).

• Scalar: ${var}
• List: @{var}
• Dictionary: &{var}
• Environment: %{var}

The list (@{variable}) and dictionary (&{variable}) syntax is optional when assigning variables. You can use the list syntax when assigning a Table to a variable, but it is unnecessary.

When doing variable assignment, it's entirely valid to assign lists and dictionaries to scalar variables like this:

The reason to use the special syntax is that Robot Framework does some extra validation for you.

Validate that the keyword returns a list (or something list-like)

Validate that the keyword returns a dictionary (or something dictionary-like)

With dictionary variables, the assignment does another thing: it turns it into a Robot Framework DotDict. A DotDict is otherwise identical to a normal Python dictionary but allows accessing values through dot-notation: ${my_dict.two}.

Note: If you assigned to @{my_list}, you can always access it through ${my_list}, and vice-versa. They refer to the same variable.

The second place where this syntax is used is when calling keywords. With list or dictionary variables, they are unpacked as arguments automatically. If you are familiar with the Python syntax *args and **kwargs, this is similar to that.

For example, here we call the first keyword in three different ways: with individual arguments, by unpacking a list, and by unpacking a dictionary:

This is also why it is used when FOR looping. These two examples are identical:

If the second FOR loop used ${names} instead of @{names}, it would not loop the names inside the list but would instead only loop once and return the list itself.

So, in conclusion: We don't use the @-syntax when assigning a Table to a variable because it is optional, but it would work because a Table is list-like. We also have to use the @-syntax when looping over a Table, because we want to loop over the rows inside of it.

Assigning variables

Expressions are evaluated using Python's eval function. All Python built-in functions are available. All unrecognized Python variables are considered to be modules that are automatically imported. It is possible to use all available Python modules, including the standard modules and any installed third party modules.

Built-in variables

Runtime variables

Environment variables available during a Control Room run

In Robot Framework syntax the environment variables are marked by % character. In Python syntax these variables can be accessed by os.getenv("ROBOT_ROOT", None).

I want to learn more!

Read more about variables in the Robot Framework User Guide.