> ## Documentation Index
> Fetch the complete documentation index at: https://codegeninc-codegen-bot-sdk-docs-2-0.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# Collections

Codegen enables traversing and manipulating collections through the [List](/api-reference/core/List) and [Dict](/api-reference/core/Dict) classes.

These APIs work consistently across Python and TypeScript while preserving formatting and structure.

## Core Concepts

The [List](/api-reference/core/List) and [Dict](/api-reference/core/Dict) classes provide a consistent interface for working with ordered sequences of elements. Key features include:

* Standard sequence operations (indexing, length, iteration)
* Automatic formatting preservation
* Safe modification operations
* Language-agnostic behavior
* Comment and whitespace preservation

Collections handle:

* Proper indentation
* Delimiters (commas, newlines)
* Multi-line formatting
* Leading/trailing whitespace
* Nested structures

## List Operations

Lists in both Python and TypeScript can be manipulated using the same APIs:

```python
# Basic operations
items_list = file.get_symbol("items").value  # Get list value
first = items_list[0]        # Access elements
length = len(items_list)     # Get length
items_list[0] = "new"       # Modify element
items_list.append("d")      # Add to end
items_list.insert(1, "x")   # Insert at position
del items_list[1]           # Remove element

# Iteration
for item in items_list:
    print(item.source)

# Bulk operations
items_list.clear()          # Remove all elements
```

### Single vs Multi-line Lists

Collections automatically preserve formatting:

```python
# Source code:
items = [a, b, c]
config = [
    "debug",
    "verbose",
    "trace",
]

# Manipulation code:
items_list = file.get_symbol("items").value
items_list.append("d")    # Adds new element

config_list = file.get_symbol("config").value
config_list.append("info")  # Adds with formatting

# Result:
items = [a, b, c, d]
config = [
    "debug",
    "verbose",
    "trace",
    "info",
]
```

## Dictionary Operations

Dictionaries provide a similar consistent interface:

```python
# Basic operations
settings = file.get_symbol("settings").value  # Get dict value
value = settings["key"]     # Get value
settings["key"] = "value"   # Set value
del settings["key"]         # Remove key
has_key = "key" in settings # Check existence

# Iteration
for key in settings:
    print(f"{key}: {settings[key]}")

# Bulk operations
settings.clear()           # Remove all entries
```