Implementation:Mistralai Client python Message Models

Knowledge Sources	Mistral Client Python Mistral AI Docs
Domains	NLP, API_Design
Last Updated	2026-02-15 14:00 GMT

Overview

Concrete tool for constructing typed conversation messages provided by the mistralai SDK's Pydantic model classes.

Description

The UserMessage, SystemMessage, and AssistantMessage classes are Pydantic models that represent individual messages in a conversation. Each accepts a content parameter (string or list of content chunks for multimodal input) and a role parameter that is auto-set based on the message type. These models validate inputs and serialize to the JSON format expected by the Mistral API.

Usage

Import these classes when constructing the message list for chat.complete(), chat.stream(), or any chat-based API call. Use SystemMessage for behavioral instructions, UserMessage for user input, and AssistantMessage for including prior model responses in multi-turn conversations.

Code Reference

Source Location

• Repository: client-python
• File: src/mistralai/client/models/usermessage.py (L1-60), systemmessage.py (L1-35), assistantmessage.py (L1-77)

Signature

class UserMessage(BaseModel):
    content: Union[str, List[ContentChunk]]
    role: Literal["user"] = "user"

class SystemMessage(BaseModel):
    content: Union[str, List[SystemMessageContentChunks]]
    role: Literal["system"] = "system"

class AssistantMessage(BaseModel):
    content: Optional[Union[str, List[ContentChunk]]] = None
    tool_calls: Optional[List[ToolCall]] = None
    prefix: Optional[bool] = None
    role: Literal["assistant"] = "assistant"

Import

from mistralai.models import UserMessage, SystemMessage, AssistantMessage

I/O Contract

Inputs

Name	Type	Required	Description
content	Union[str, List[ContentChunk]]	Yes	Text string or multimodal content chunks
role	Literal["user"/"system"/"assistant"]	No	Auto-set by message class

Outputs

Name	Type	Description
Message object	UserMessage / SystemMessage / AssistantMessage	Validated Pydantic model ready for API serialization

Usage Examples

Basic Text Messages

from mistralai.models import UserMessage, SystemMessage

messages = [
    SystemMessage(content="You are a helpful coding assistant."),
    UserMessage(content="Explain Python decorators."),
]

Multi-turn Conversation

from mistralai.models import UserMessage, SystemMessage, AssistantMessage

messages = [
    SystemMessage(content="You are a math tutor."),
    UserMessage(content="What is 2+2?"),
    AssistantMessage(content="2+2 equals 4."),
    UserMessage(content="And 3+3?"),
]

Related Pages

Implements Principle

• Principle:Mistralai_Client_python_Message_Construction