Environment variables could be useful for handling application **settings**, as part of the **installation** of Python, etc.

## Create and Use Env Vars { #create-and-use-env-vars }

You can **create** and use environment variables in the **shell (terminal)**, without needing Python:

//// tab | Linux, macOS, Windows Bash

<div class="termy">

```console

type CheckConstraint struct {
	Name       string
	Constraint string // length(phone) >= 10
	*Field
}

func (chk *CheckConstraint) GetName() string { return chk.Name }

func (chk *CheckConstraint) Build() (sql string, vars []interface{}) {
	return "CONSTRAINT ? CHECK (?)", []interface{}{clause.Column{Name: chk.Name}, clause.Expr{SQL: chk.Constraint}}
}

// ParseCheckConstraints parse schema check constraints

## Conditional OpenAPI from settings and env vars { #conditional-openapi-from-settings-and-env-vars }

You can easily use the same Pydantic settings to configure your generated OpenAPI and the docs UIs.

For example:

{* ../../docs_src/conditional_openapi/tutorial001_py39.py hl[6,11] *}

		apiErr.Description = fmt.Sprintf("unable to perform in-place update, release time is unrecognized: %s", currentReleaseTime)
		writeErrorResponseJSON(ctx, w, apiErr, r.URL)
		return
	}

	vars := mux.Vars(r)
	updateURL := vars["updateURL"]
	dryRun := r.Form.Get("dry-run") == "true"

	mode := getMinioMode()
	if updateURL == "" {
		updateURL = minioReleaseInfoURL
		if runtime.GOOS == globalWindowsOSName {

	ctx := r.Context()

	objectAPI, _ := validateAdminReq(ctx, w, r, policy.SiteReplicationOperationAction)
	if objectAPI == nil {
		return
	}

	vars := mux.Vars(r)
	bucket := vars["bucket"]
	operation := madmin.BktOp(vars["operation"])

	var err error
	switch operation {
	default:
		err = errSRInvalidRequest(errInvalidArgument)
	case madmin.MakeWithVersioningBktOp:

			tx.Statement.AddClause(clause.Select{
				Distinct:   db.Statement.Distinct,
				Expression: clause.Expr{SQL: v, Vars: args},
			})
		} else if strings.Count(v, "@") > 0 && len(args) > 0 {
			tx.Statement.AddClause(clause.Select{
				Distinct:   db.Statement.Distinct,
				Expression: clause.NamedExpr{SQL: v, Vars: args},
			})
		} else {
			tx.Statement.Selects = []string{v}

			for _, arg := range args {

package callbacks

import (
	"gorm.io/gorm"
)

func RawExec(db *gorm.DB) {
	if db.Error == nil && !db.DryRun {
		result, err := db.Statement.ConnPool.ExecContext(db.Statement.Context, db.Statement.SQL.String(), db.Statement.Vars...)
		if err != nil {
			db.AddError(err)
			return
		}

		db.RowsAffected, _ = result.RowsAffected()

		if db.Statement.Result != nil {
			db.Statement.Result.Result = result

		if !db.DryRun && db.Error == nil {
			ok, mode := hasReturning(db, supportReturning)
			if !ok {
				result, err := db.Statement.ConnPool.ExecContext(db.Statement.Context, db.Statement.SQL.String(), db.Statement.Vars...)

				if db.AddError(err) == nil {
					db.RowsAffected, _ = result.RowsAffected()

					if db.Statement.Result != nil {
						db.Statement.Result.Result = result

package schema

import (
	"gorm.io/gorm/clause"
)

// ConstraintInterface database constraint interface
type ConstraintInterface interface {
	GetName() string
	Build() (sql string, vars []interface{})
}

// GormDataTypeInterface gorm data type interface
type GormDataTypeInterface interface {
	GormDataType() string
}

// FieldNewValuePool field new scan value pool
type FieldNewValuePool interface {
	Get() interface{}

// present or if one configuration is incomplete.
func IsPresent() (bool, error) {
	// isPresent reports whether at least one of the
	// given env. variables is present.
	isPresent := func(vars ...string) bool {
		for _, v := range vars {
			if _, ok := os.LookupEnv(v); ok {
				return ok
			}
		}
		return false
	}

	// First, check which KMS/KES env. variables are present.