Python XSD Restrictions, Facets & Pattern Matching (Regex)

In Plain English

XSD restrictions (facets) define acceptable boundaries for element and attribute values. You can restrict numeric ranges (minInclusive, maxInclusive), define allowed string enumerations (enumeration), constrain lengths, and enforce regular expression patterns (pattern).

The Mental Model

"Restrictions are the velvet rope bouncers of your data schema: they verify that an age is between 18 and 120, a password matches a regex pattern, or a currency code is strictly USD, EUR, or GBP."

Deep Dive: How It Works

<xs:restriction base="xs:string">: Base type being constrained.

<xs:enumeration value="..."/>: Constrains value to an explicit set of allowable choices.

<xs:pattern value="[0-9]{3}-[A-Z]{2}"/>: Validates against a regular expression pattern.

Numeric Facets: <xs:minInclusive value="0"/> and <xs:maxInclusive value="100"/>.

Syntax Blueprint

<xs:simpleType name="AgeType">
  <xs:restriction base="xs:integer">
    <xs:minInclusive value="18" />
  </xs:restriction>
</xs:simpleType>

Creates a custom simple type requiring integer values >= 18.

Core Rules to Remember

Value Constraining: Enforces business rules directly at the schema validation layer.

Enumerations: Limits values to specific allowed enum constants (e.g. pending, approved, rejected).

Regex Patterns: Enforces exact formats for postal codes, phone numbers, and SKUs.

Common Beginner Traps & How to Fix Them

Mistake:Applying string length facets to integer types.

Why it happens: <xs:length> applies to strings; numeric types must use <xs:totalDigits> or <xs:maxInclusive>.

How to fix: Use the correct facet for the base data type.

Pro Tip: Use <xs:whiteSpace value="collapse"/> to automatically strip leading, trailing, and duplicate whitespace before validation.

Live Interactive Example

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Restricted Password and Status Schema

XML 1.0 / XSD

Live Browser Preview

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How it works: Enforces strict enum values and formatted SKU codes matching [A-Z]{3}-[0-9]{4}.

Your Turn: Micro Challenge

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Micro Exercise

Define an integer score restriction

Create a <xs:restriction base="xs:integer"> with <xs:minInclusive value="0"/> and <xs:maxInclusive value="100"/>.

Sandbox Output

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Deep Dive: How It Works

<xs:restriction base="xs:string">: Base type being constrained.

<xs:enumeration value="..."/>: Constrains value to an explicit set of allowable choices.

<xs:pattern value="[0-9]{3}-[A-Z]{2}"/>: Validates against a regular expression pattern.

Numeric Facets: <xs:minInclusive value="0"/> and <xs:maxInclusive value="100"/>.