cloup.constraints

Constraints for parameter groups.

New in version v0.5.0.

Classes

If(condition, then[, else_])

Checks one constraint or another depending on the truth value of the condition.

AcceptAtMost(n)

Satisfied if the number of set parameters is <= n.

AcceptBetween(min, max)

Satisfied if the number of set parameters is between min and max (included).

And(*constraints)

It’s satisfied if all operands are satisfied.

Constraint()

A constraint that can be checked against an arbitrary collection of CLI parameters with respect to a specific click.Context (which contains the values assigned to the parameters in ctx.params).

ErrorFmt()

Rephraser allows you to pass a format string as error argument; this class contains the “replacement fields” supported by such format string. You can use them as following::.

Operator(*constraints)

Base class for all n-ary operators defined on constraints.

Or(*constraints)

It’s satisfied if at least one of the operands is satisfied.

Rephraser(constraint[, help, error])

A constraint decorator that can override the help and/or the error message of the wrapped constraint.

RequireAtLeast(n)

Satisfied if the number of set parameters is >= n.

RequireExactly(n)

Requires an exact number of parameters to be set.

WrapperConstraint(constraint, **attrs)

Abstract class that wraps another constraint and delegates all methods to it.

BoundConstraintSpec(constraint, param_names)

A NamedTuple storing a Constraint and the names of the parameters it has to check.

ConstraintMixin(*args[, constraints, …])

Provides support for constraints.

AllSet(*param_names)

True if all listed parameters are set.

AnySet(*param_names)

True if any of the listed parameters is set.

Equal(param_name, value)

True if the parameter value equals value.

IsSet(param_name)

True if the parameter is set.

Not(predicate)

Logical NOT of a predicate.

Functions

constrained_params(constr, *param_adders)

Return a decorator that adds the given parameters and applies a constraint to them. Equivalent to::.

constraint(constr, params)

Register a constraint on a list of parameters specified by (destination) name (e.g.

Attributes

ErrorRephraser

HelpRephraser

accept_none

Satisfied if none of the parameters is set. Useful only in conditional constraints.

all_or_none

Satisfied if either all or none of the parameters are set.

mutually_exclusive

Satisfied if at most one of the parameters is set.

require_all

Satisfied if all parameters are set.

require_any

Alias for RequireAtLeast(1).

require_one

Alias for RequireExactly(1).

Contents

class cloup.constraints.If(condition, then, else_=None)[source]

Bases: cloup.constraints._core.Constraint

Checks one constraint or another depending on the truth value of the condition.

New in version 0.8.0: you can now pass a sequence of parameter names as condition, which corresponds to the predicate AllSet(*param_names).

Parameters
help(self, ctx)[source]

A description of the constraint.

Parameters

ctx (click.Context) –

Return type

str

check_consistency(self, params)[source]

Perform some sanity checks that detect inconsistencies between these constraints and the properties of the input parameters (e.g. required).

For example, a constraint that requires the parameters to be mutually exclusive is not consistent with a group of parameters with multiple required options.

These sanity checks are meant to catch developer’s mistakes and don’t depend on the values assigned to the parameters; therefore:

  • they can be performed before any parameter parsing

  • they can be disabled in production (setting check_constraints_consistency=False in context_settings)

Parameters

params (Sequence[click.Parameter]) – list of click.Parameter instances

Raises

UnsatisfiableConstraint if the constraint cannot be satisfied independently from the values provided by the user

Return type

None

check_values(self, params, ctx)[source]

Check that the constraint is satisfied by the input parameters in the given context, which (among other things) contains the values assigned to the parameters in ctx.params.

You probably don’t want to call this method directly. Use check() instead.

Parameters
Raises

ConstraintViolated

Return type

None

__repr__(self)[source]

Return repr(self).

Return type

str

class cloup.constraints.AcceptAtMost(n)[source]

Bases: Constraint

Satisfied if the number of set parameters is <= n.

Parameters

n (int) –

help(self, ctx)[source]

A description of the constraint.

Parameters

ctx (click.Context) –

Return type

str

check_consistency(self, params)[source]

Perform some sanity checks that detect inconsistencies between these constraints and the properties of the input parameters (e.g. required).

For example, a constraint that requires the parameters to be mutually exclusive is not consistent with a group of parameters with multiple required options.

These sanity checks are meant to catch developer’s mistakes and don’t depend on the values assigned to the parameters; therefore:

  • they can be performed before any parameter parsing

  • they can be disabled in production (setting check_constraints_consistency=False in context_settings)

Parameters

params (Sequence[click.Parameter]) – list of click.Parameter instances

Raises

UnsatisfiableConstraint if the constraint cannot be satisfied independently from the values provided by the user

Return type

None

check_values(self, params, ctx)[source]

Check that the constraint is satisfied by the input parameters in the given context, which (among other things) contains the values assigned to the parameters in ctx.params.

You probably don’t want to call this method directly. Use check() instead.

Parameters
Raises

ConstraintViolated

Return type

None

__repr__(self)[source]

Return repr(self).

Return type

str

class cloup.constraints.AcceptBetween(min, max)[source]

Bases: WrapperConstraint

Abstract class that wraps another constraint and delegates all methods to it. Useful when you want to define a parametric constraint combining other existing constraints minimizing the boilerplate.

This is an alternative to defining a function and using Rephraser. Feel free to do that in your code, but cloup will stick to the convention that parametric constraints are defined as classes and written in camel-case.

Satisfied if the number of set parameters is between min and max (included).

Parameters
  • min (int) – must be an integer >= 0

  • max (int) – must be an integer > min

help(self, ctx)[source]

A description of the constraint.

Parameters

ctx (click.Context) –

Return type

str

class cloup.constraints.And(*constraints)[source]

Bases: Operator

It’s satisfied if all operands are satisfied.

N-ary operator for constraints. :param constraints: operands

Parameters

constraints (cloup.constraints._core.Constraint) –

HELP_SEP =  and
check_values(self, params, ctx)[source]

Check that the constraint is satisfied by the input parameters in the given context, which (among other things) contains the values assigned to the parameters in ctx.params.

You probably don’t want to call this method directly. Use check() instead.

Parameters
Raises

ConstraintViolated

Return type

None

__and__(self, other)[source]
Parameters

other (Constraint) –

Return type

And

class cloup.constraints.Constraint[source]

Bases: abc.ABC

A constraint that can be checked against an arbitrary collection of CLI parameters with respect to a specific click.Context (which contains the values assigned to the parameters in ctx.params).

Changed in version 0.9.0: calling a constraint, previously equivalent to check(), is now equivalent to calling cloup.constrained_params() with this constraint as first argument.

static must_check_consistency(ctx)[source]

Return True if consistency checks are enabled.

Changed in version 0.9.0: this method now a static method and takes a click.Context in input.

Parameters

ctx (click.Context) –

Return type

bool

__getattr__(self, attr)[source]
Parameters

attr (str) –

Return type

Any

abstract help(self, ctx)[source]

A description of the constraint.

Parameters

ctx (click.Context) –

Return type

str

check_consistency(self, params)[source]

Perform some sanity checks that detect inconsistencies between these constraints and the properties of the input parameters (e.g. required).

For example, a constraint that requires the parameters to be mutually exclusive is not consistent with a group of parameters with multiple required options.

These sanity checks are meant to catch developer’s mistakes and don’t depend on the values assigned to the parameters; therefore:

  • they can be performed before any parameter parsing

  • they can be disabled in production (setting check_constraints_consistency=False in context_settings)

Parameters

params (Sequence[click.Parameter]) – list of click.Parameter instances

Raises

UnsatisfiableConstraint if the constraint cannot be satisfied independently from the values provided by the user

Return type

None

abstract check_values(self, params, ctx)[source]

Check that the constraint is satisfied by the input parameters in the given context, which (among other things) contains the values assigned to the parameters in ctx.params.

You probably don’t want to call this method directly. Use check() instead.

Parameters
Raises

ConstraintViolated

Return type

None

check(self, params: Sequence[click.Parameter], ctx: Optional[click.Context] = None)None[source]
check(self, params: Sequence[str], ctx: Optional[click.Context] = None)None

Raise an exception if the constraint is not satisfied by the input parameters in the given (or current) context.

This method calls both check_consistency() (if enabled) and check_values().

Tip

By default check_consistency() is called since it shouldn’t have any performance impact. Nonetheless, you can disable it in production passing check_constraints_consistency=False as part of your context_settings.

Parameters
Raises

ConstraintViolated UnsatisfiableConstraint

rephrased(self, help=None, error=None)[source]

Override the help string and/or the error message of this constraint wrapping it with a Rephraser.

Parameters
  • help (Union[None, str, HelpRephraser]) – if provided, overrides the help string of this constraint. It can be a string or a function (ctx: click.Context, constr: Constraint) -> str. If you want to hide this constraint from the help, pass help="".

  • error (Union[None, str, ErrorRephraser]) –

    if provided, overrides the error message of this constraint. It can be:

    • a string, eventually a format string supporting the replacement fields described in ErrorFmt.

    • or a function (err: ConstraintViolated) -> str; note that a ConstraintViolated error has fields for ctx, constraint and params, so it’s a complete description of what happened.

Return type

Rephraser

hidden(self)[source]

Hide this constraint from the command help.

Return type

Rephraser

__call__(self, *param_adders)[source]

Equivalent to calling cloup.constrained_params() with this constraint as first argument.

Changed in version 0.9.0: this method, previously equivalent to check(), is now equivalent to calling cloup.constrained_params() with this constraint as first argument.

Parameters

param_adders (cloup.typing.Decorator) –

Return type

Callable[[cloup.typing.F], cloup.typing.F]

__or__(self, other)[source]
Parameters

other (Constraint) –

Return type

Or

__and__(self, other)[source]
Parameters

other (Constraint) –

Return type

And

__repr__(self)[source]

Return repr(self).

Return type

str

class cloup.constraints.ErrorFmt[source]

Bases: cloup._util.FrozenSpace

Rephraser allows you to pass a format string as error argument; this class contains the “replacement fields” supported by such format string. You can use them as following:

mutually_exclusive.rephrased(
    error=f"{ErrorFmt.error}\n"
          f"Some extra information here."
)
Return type

None

error = {error}

Replaced by the original error message. Useful if all you want is to append or prepend some extra info to the original error message.

param_list = {param_list}

Replaced by a 2-space indented list of the constrained parameters.

cloup.constraints.ErrorRephraser
cloup.constraints.HelpRephraser
class cloup.constraints.Operator(*constraints)[source]

Bases: Constraint, abc.ABC

Base class for all n-ary operators defined on constraints.

N-ary operator for constraints. :param constraints: operands

Parameters

constraints (cloup.constraints._core.Constraint) –

HELP_SEP :str

Used as separator of all constraints’ help strings.

help(self, ctx)[source]

A description of the constraint.

Parameters

ctx (click.Context) –

Return type

str

check_consistency(self, params)[source]

Perform some sanity checks that detect inconsistencies between these constraints and the properties of the input parameters (e.g. required).

For example, a constraint that requires the parameters to be mutually exclusive is not consistent with a group of parameters with multiple required options.

These sanity checks are meant to catch developer’s mistakes and don’t depend on the values assigned to the parameters; therefore:

  • they can be performed before any parameter parsing

  • they can be disabled in production (setting check_constraints_consistency=False in context_settings)

Parameters

params (Sequence[click.Parameter]) – list of click.Parameter instances

Raises

UnsatisfiableConstraint if the constraint cannot be satisfied independently from the values provided by the user

Return type

None

__repr__(self)[source]

Return repr(self).

Return type

str

class cloup.constraints.Or(*constraints)[source]

Bases: Operator

It’s satisfied if at least one of the operands is satisfied.

N-ary operator for constraints. :param constraints: operands

Parameters

constraints (cloup.constraints._core.Constraint) –

HELP_SEP =  or
check_values(self, params, ctx)[source]

Check that the constraint is satisfied by the input parameters in the given context, which (among other things) contains the values assigned to the parameters in ctx.params.

You probably don’t want to call this method directly. Use check() instead.

Parameters
Raises

ConstraintViolated

Return type

None

__or__(self, other)[source]
Parameters

other (Constraint) –

Return type

Or

class cloup.constraints.Rephraser(constraint, help=None, error=None)[source]

Bases: Constraint

A constraint decorator that can override the help and/or the error message of the wrapped constraint.

You’ll rarely (if ever) use this class directly. In most cases, you’ll use the method Constraint.rephrased(). Refer to it for more info.

See also

Parameters
help(self, ctx)[source]

A description of the constraint.

Parameters

ctx (click.Context) –

Return type

str

check_consistency(self, params)[source]

Perform some sanity checks that detect inconsistencies between these constraints and the properties of the input parameters (e.g. required).

For example, a constraint that requires the parameters to be mutually exclusive is not consistent with a group of parameters with multiple required options.

These sanity checks are meant to catch developer’s mistakes and don’t depend on the values assigned to the parameters; therefore:

  • they can be performed before any parameter parsing

  • they can be disabled in production (setting check_constraints_consistency=False in context_settings)

Parameters

params (Sequence[click.Parameter]) – list of click.Parameter instances

Raises

UnsatisfiableConstraint if the constraint cannot be satisfied independently from the values provided by the user

Return type

None

check_values(self, params, ctx)[source]

Check that the constraint is satisfied by the input parameters in the given context, which (among other things) contains the values assigned to the parameters in ctx.params.

You probably don’t want to call this method directly. Use check() instead.

Parameters
Raises

ConstraintViolated

Return type

None

__repr__(self)[source]

Return repr(self).

Return type

str

class cloup.constraints.RequireAtLeast(n)[source]

Bases: Constraint

Satisfied if the number of set parameters is >= n.

Parameters

n (int) –

help(self, ctx)[source]

A description of the constraint.

Parameters

ctx (click.Context) –

Return type

str

check_consistency(self, params)[source]

Perform some sanity checks that detect inconsistencies between these constraints and the properties of the input parameters (e.g. required).

For example, a constraint that requires the parameters to be mutually exclusive is not consistent with a group of parameters with multiple required options.

These sanity checks are meant to catch developer’s mistakes and don’t depend on the values assigned to the parameters; therefore:

  • they can be performed before any parameter parsing

  • they can be disabled in production (setting check_constraints_consistency=False in context_settings)

Parameters

params (Sequence[click.Parameter]) – list of click.Parameter instances

Raises

UnsatisfiableConstraint if the constraint cannot be satisfied independently from the values provided by the user

Return type

None

check_values(self, params, ctx)[source]

Check that the constraint is satisfied by the input parameters in the given context, which (among other things) contains the values assigned to the parameters in ctx.params.

You probably don’t want to call this method directly. Use check() instead.

Parameters
Raises

ConstraintViolated

Return type

None

__repr__(self)[source]

Return repr(self).

Return type

str

class cloup.constraints.RequireExactly(n)[source]

Bases: WrapperConstraint

Requires an exact number of parameters to be set.

Parameters
  • constraint – the constraint to wrap

  • attrs – these are just used to generate a __repr__ method

  • n (int) –

help(self, ctx)[source]

A description of the constraint.

Parameters

ctx (click.Context) –

Return type

str

check_values(self, params, ctx)[source]

Check that the constraint is satisfied by the input parameters in the given context, which (among other things) contains the values assigned to the parameters in ctx.params.

You probably don’t want to call this method directly. Use check() instead.

Parameters
Raises

ConstraintViolated

Return type

None

__repr__(self)[source]

Return repr(self).

Return type

str

class cloup.constraints.WrapperConstraint(constraint, **attrs)[source]

Bases: Constraint

Abstract class that wraps another constraint and delegates all methods to it. Useful when you want to define a parametric constraint combining other existing constraints minimizing the boilerplate.

This is an alternative to defining a function and using Rephraser. Feel free to do that in your code, but cloup will stick to the convention that parametric constraints are defined as classes and written in camel-case.

Parameters
help(self, ctx)[source]

A description of the constraint.

Parameters

ctx (click.Context) –

Return type

str

check_consistency(self, params)[source]

Perform some sanity checks that detect inconsistencies between these constraints and the properties of the input parameters (e.g. required).

For example, a constraint that requires the parameters to be mutually exclusive is not consistent with a group of parameters with multiple required options.

These sanity checks are meant to catch developer’s mistakes and don’t depend on the values assigned to the parameters; therefore:

  • they can be performed before any parameter parsing

  • they can be disabled in production (setting check_constraints_consistency=False in context_settings)

Parameters

params (Sequence[click.Parameter]) – list of click.Parameter instances

Raises

UnsatisfiableConstraint if the constraint cannot be satisfied independently from the values provided by the user

Return type

None

check_values(self, params, ctx)[source]

Check that the constraint is satisfied by the input parameters in the given context, which (among other things) contains the values assigned to the parameters in ctx.params.

You probably don’t want to call this method directly. Use check() instead.

Parameters
Raises

ConstraintViolated

Return type

None

__repr__(self)[source]

Return repr(self).

Return type

str

cloup.constraints.accept_none

Satisfied if none of the parameters is set. Useful only in conditional constraints.

cloup.constraints.all_or_none

Satisfied if either all or none of the parameters are set.

cloup.constraints.mutually_exclusive

Satisfied if at most one of the parameters is set.

cloup.constraints.require_all

Satisfied if all parameters are set.

cloup.constraints.require_any

Alias for RequireAtLeast(1).

cloup.constraints.require_one

Alias for RequireExactly(1).

class cloup.constraints.BoundConstraintSpec[source]

Bases: NamedTuple

A NamedTuple storing a Constraint and the names of the parameters it has to check.

Parameters
constraint :cloup.constraints._core.Constraint
param_names :Union[Sequence[str]]
resolve_params(self, cmd)[source]
Parameters

cmd (ConstraintMixin) –

Return type

BoundConstraint

class cloup.constraints.ConstraintMixin(*args, constraints=(), show_constraints=None, **kwargs)[source]

Provides support for constraints.

Parameters
  • constraints (Sequence[Union[cloup.constraints._support.BoundConstraintSpec, cloup.constraints._support.BoundConstraint]]) – sequence of constraints bound to specific groups of parameters. Note that constraints applied to option groups are collected from the option groups themselves, so they don’t need to be included in this argument.

  • show_constraints (Optional[bool]) – whether to include a “Constraint” section in the command help. This is also available as a context setting having a lower priority than this attribute.

  • args (Any) – positional arguments forwarded to the next class in the MRO

  • kwargs (Any) – keyword arguments forwarded to the next class in the MRO

optgroup_constraints

Constraints applied to OptionGroup instances.

param_constraints :Tuple[BoundConstraint, Ellipsis]

Constraints registered using @constraint (or equivalent method).

all_constraints

All constraints applied to parameter/option groups of this command.

parse_args(self, ctx, args)[source]
Parameters
Return type

List[str]

get_param_by_name(self, name)[source]
Parameters

name (str) –

Return type

click.Parameter

get_params_by_name(self, names)[source]
Parameters

names (Iterable[str]) –

Return type

Sequence[click.Parameter]

format_constraints(self, ctx, formatter)[source]
Parameters
Return type

None

must_show_constraints(self, ctx)[source]
Parameters

ctx (click.Context) –

Return type

bool

cloup.constraints.constrained_params(constr, *param_adders)[source]

Return a decorator that adds the given parameters and applies a constraint to them. Equivalent to:

@param_adders[0]
...
@param_adders[-1]
@constraint(constr, <param names>)

This decorator saves you to manually (re)type the parameter names. It can also be used inside @option_group.

Instead of using this decorator, you can also call the constraint itself:

@constr(*param_adders)

but remember that:

  • Python 3.9 is the first that allows arbitrary expressions on the right of @;

  • using a long conditional/composite constraint as decorator may be less readable.

In these cases, you may consider using @constrained_params.

New in version 0.9.0.

Parameters
  • constr (cloup.constraints._core.Constraint) – an instance of Constraint

  • param_adders (Callable[[Callable[[..], Any]], Callable[[..], Any]]) – function decorators, each attaching a single parameter to the decorated function.

Return type

Callable[[F], F]

cloup.constraints.constraint(constr, params)[source]

Register a constraint on a list of parameters specified by (destination) name (e.g. the default name of --input-file is input_file).

Parameters
Return type

Callable[[F], F]

class cloup.constraints.AllSet(*param_names)[source]

Bases: Predicate

True if all listed parameters are set.

New in version 0.8.0.

Parameters

param_names (str) –

negated_description(self, ctx)[source]

Succinct description of the negation of this predicate (alias: neg_desc).

Parameters

ctx (click.Context) –

Return type

str

description(self, ctx)[source]

Succinct description of the predicate (alias: desc).

Parameters

ctx (click.Context) –

Return type

str

__call__(self, ctx)[source]

Evaluate the predicate on the given context.

Parameters

ctx (click.Context) –

Return type

bool

__and__(self, other)[source]
Parameters

other (Predicate) –

Return type

Predicate

class cloup.constraints.AnySet(*param_names)[source]

Bases: Predicate

True if any of the listed parameters is set.

New in version 0.8.0.

Parameters

param_names (str) –

negated_description(self, ctx)[source]

Succinct description of the negation of this predicate (alias: neg_desc).

Parameters

ctx (click.Context) –

Return type

str

description(self, ctx)[source]

Succinct description of the predicate (alias: desc).

Parameters

ctx (click.Context) –

Return type

str

__call__(self, ctx)[source]

Evaluate the predicate on the given context.

Parameters

ctx (click.Context) –

Return type

bool

__or__(self, other)[source]
Parameters

other (Predicate) –

Return type

Predicate

class cloup.constraints.Equal(param_name, value)[source]

Bases: Predicate

True if the parameter value equals value.

Parameters
  • param_name (str) –

  • value (Any) –

description(self, ctx)[source]

Succinct description of the predicate (alias: desc).

Parameters

ctx (click.Context) –

Return type

str

negated_description(self, ctx)[source]

Succinct description of the negation of this predicate (alias: neg_desc).

Parameters

ctx (click.Context) –

Return type

str

__call__(self, ctx)[source]

Evaluate the predicate on the given context.

Parameters

ctx (click.Context) –

Return type

bool

class cloup.constraints.IsSet(param_name)[source]

Bases: Predicate

True if the parameter is set.

Parameters

param_name (str) –

description(self, ctx)[source]

Succinct description of the predicate (alias: desc).

Parameters

ctx (click.Context) –

Return type

str

negated_description(self, ctx)[source]

Succinct description of the negation of this predicate (alias: neg_desc).

Parameters

ctx (click.Context) –

Return type

str

__call__(self, ctx)[source]

Evaluate the predicate on the given context.

Parameters

ctx (click.Context) –

Return type

bool

__and__(self, other)[source]
Parameters

other (Predicate) –

Return type

Predicate

__or__(self, other)[source]
Parameters

other (Predicate) –

Return type

Predicate

class cloup.constraints.Not(predicate)[source]

Bases: Predicate, Generic[P]

Logical NOT of a predicate.

Parameters

predicate (P) –

description(self, ctx)[source]

Succinct description of the predicate (alias: desc).

Parameters

ctx (click.Context) –

Return type

str

negated_description(self, ctx)[source]

Succinct description of the negation of this predicate (alias: neg_desc).

Parameters

ctx (click.Context) –

Return type

str

__call__(self, ctx)[source]

Evaluate the predicate on the given context.

Parameters

ctx (click.Context) –

Return type

bool

__invert__(self)[source]
Return type

P

__repr__(self)[source]

Return repr(self).

Return type

str

exception cloup.constraints.ConstraintViolated(message, ctx, constraint, params)[source]

Bases: click.UsageError

An internal exception that signals a usage error. This typically aborts any further handling.

Parameters

Initialize self. See help(type(self)) for accurate signature.

classmethod default(cls, desc, ctx, constraint, params)[source]
Parameters
Return type

ConstraintViolated

exception cloup.constraints.UnsatisfiableConstraint(constraint, params, reason)[source]

Bases: Exception

Raised if a constraint cannot be satisfied by a group of parameters independently from their values at runtime; e.g. mutually_exclusive cannot be satisfied if multiple of the parameters are required.

Initialize self. See help(type(self)) for accurate signature.

Parameters