Codegen’s enables manipulation of variable assignments via the following classes:

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Simple Value Changes

Consider the following source code: 
const userId = 123;
const [userName, userAge] = ["Eve", 25];
In Codegen, you can access assignments with the get_local_var_assignment method. You can then manipulate the assignment with the set_value method. 
id_assignment = file.code_block.get_local_var_assignment("userId")
id_assignment.set_value("456")

name_assignment = file.code_block.get_local_var_assignment("name")
name_assignment.rename("userName")
Assignments inherit both HasName and HasValue behaviors. See Inheritable Behaviors for more details.

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Type Annotations

Similarly, you can set type annotations with the set_type_annotation method. For example, consider the following source code: 
let status;
const data = fetchData();
You can manipulate the assignments as follows: 
status_assignment = file.code_block.get_local_var_assignment("status")
status_assignment.set_type_annotation("Status")
status_assignment.set_value("Status.ACTIVE")

data_assignment = file.code_block.get_local_var_assignment("data")
data_assignment.set_type_annotation("ResponseData<T>")

# Result:
let status: Status = Status.ACTIVE;
const data: ResponseData<T> = fetchData();

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Tracking Usages and Dependencies

Like other symbols, Assignments support usages and dependencies. 
assignment = file.code_block.get_local_var_assignment("userId")

# Get all usages of the assignment
usages = assignment.usages

# Get all dependencies of the assignment
dependencies = assignment.dependencies
See Dependencies and Usages for more details.