Which statements are correct about a group

Users should generally never rely on a pattern being evaluated. Depending on implementation, the interpreter may cache values or use other optimizations which skip repeated evaluations. In this case, if flag is a guard. Read more about that in the next section. A guard which is part of the case must succeed for code inside the case block to execute. It takes the form: if followed by an expression.

The logical flow of a case block with a guard follows:. Check that the pattern in the case block succeeded. If the pattern failed, the guard is not evaluated and the next case block is checked. If the pattern succeeded, evaluate the guard.

If the guard condition evaluates as true, the case block is selected. If the guard condition evaluates as false, the case block is not selected. If the guard raises an exception during evaluation, the exception bubbles up. Guards are allowed to have side effects as they are expressions. Guard evaluation must stop once a case block is selected. An irrefutable case block is a match-all case block. A match statement may have at most one irrefutable case block, and it must be last.

A case block is considered irrefutable if it has no guard and its pattern is irrefutable. A pattern is considered irrefutable if we can prove from its syntax alone that it will always succeed. Only the following patterns are irrefutable:. AS Patterns whose left-hand side is irrefutable. OR Patterns containing at least one irrefutable pattern. Capture Patterns. Wildcard Patterns.

RULE is shorthand for a negative lookahead assertion. The top-level syntax for patterns is:. Note that these descriptions are purely for illustration purposes and may not reflect the underlying implementation. Furthermore, they do not cover all valid forms. An OR pattern is two or more patterns separated by vertical bars. Only the final subpattern may be irrefutable , and each subpattern must bind the same set of names to avoid ambiguity. An OR pattern matches each of its subpatterns in turn to the subject value, until one succeeds.

The OR pattern is then considered successful. Otherwise, if none of the subpatterns succeed, the OR pattern fails. In simple terms, P1 P An AS pattern matches an OR pattern on the left of the as keyword against a subject.

If the OR pattern fails, the AS pattern fails. Otherwise, the AS pattern binds the subject to the name on the right of the as keyword and succeeds. A literal pattern corresponds to most literals in Python. Triple-quoted strings are supported.

Raw strings and byte strings are supported. Formatted string literals are not supported. For the singletons None , True and False , the is operator is used. In a given pattern, a given name can only be bound once. Capture patterns always succeed. It is an identifier, as usual, even within match subject expressions, guard s, and case blocks. The dotted name in the pattern is looked up using standard Python name resolution rules. In simple terms NAME1. If the same value occurs multiple times in the same match statement, the interpreter may cache the first value found and reuse it rather than repeat the same lookup.

This cache is strictly tied to a given execution of a given match statement. A group pattern allows users to add parentheses around patterns to emphasize the intended grouping. Otherwise, it has no additional syntax. In simple terms P has the same effect as P. A sequence pattern contains several subpatterns to be matched against sequence elements. The syntax is similar to the unpacking of a list or tuple. There is no difference if parentheses or square brackets are used for sequence patterns i.

A single pattern enclosed in parentheses without a trailing comma e. While a single pattern enclosed in square brackets e. At most one star subpattern may be in a sequence pattern. The star subpattern may occur in any position. If no star subpattern is present, the sequence pattern is a fixed-length sequence pattern; otherwise it is a variable-length sequence pattern.

If the subject value is not a sequence 2 , the sequence pattern fails. If the subject value is an instance of str , bytes or bytearray the sequence pattern fails. If the length of the subject sequence is not equal to the number of subpatterns, the sequence pattern fails.

Subpatterns in the sequence pattern are matched to their corresponding items in the subject sequence from left to right. Matching stops as soon as a subpattern fails. If all subpatterns succeed in matching their corresponding item, the sequence pattern succeeds. If the length of the subject sequence is less than the number of non-star subpatterns, the sequence pattern fails.

The leading non-star subpatterns are matched to their corresponding items as for fixed-length sequences. If the previous step succeeds, the star subpattern matches a list formed of the remaining subject items, excluding the remaining items corresponding to non-star subpatterns following the star subpattern. Remaining non-star subpatterns are matched to their corresponding subject items, as for a fixed-length sequence.

The length of the subject sequence is obtained via len i. This length may be cached by the interpreter in a similar manner as value patterns. A mapping pattern contains one or more key-value patterns.

The syntax is similar to the construction of a dictionary. At most one double star pattern may be in a mapping pattern. The double star pattern must be the last subpattern in the mapping pattern. Duplicate keys in mapping patterns are disallowed.

Duplicate literal keys will raise a SyntaxError. Two keys that otherwise have the same value will raise a ValueError at runtime. If the subject value is not a mapping 3 ,the mapping pattern fails. If every key given in the mapping pattern is present in the subject mapping, and the pattern for each key matches the corresponding item of the subject mapping, the mapping pattern succeeds.

If duplicate keys are detected in the mapping pattern, the pattern is considered invalid. A SyntaxError is raised for duplicate literal values; or a ValueError for named keys of the same value.

If no pattern arguments are present, the pattern succeeds. Otherwise, the subsequent steps depend on whether keyword or positional argument patterns are present. For a number of built-in types specified below , a single positional subpattern is accepted which will match the entire subject; for these types keyword patterns also work as for other types.

If this raises an exception other than AttributeError , the exception bubbles up. If this raises AttributeError , the class pattern has failed. If this fails, the class pattern fails; if this succeeds, the match proceeds to the next keyword. If the returned value is not a tuple, the conversion fails and TypeError is raised.

If there are more positional patterns than len cls. If there are duplicate keywords, TypeError is raised. Customizing positional arguments in class pattern matching. These classes accept a single positional argument, and the pattern there is matched against the whole object rather than an attribute. For example int 0 1 matches the value 0 , but not the values 0. A function definition defines a user-defined function object see section The standard type hierarchy :.

A function definition is an executable statement. Its execution binds the function name in the current local namespace to a function object a wrapper around the executable code for the function. This function object contains a reference to the current global namespace as the global namespace to be used when the function is called. The function definition does not execute the function body; this gets executed only when the function is called.

Signup with Email. Gender Male Female. Create Account. Already Have an Account? Which statements are correct about the following disaccharide? Correct answer is option 'A'. Can you explain this answer?

Answer to Question. Sonu Choudhary Jul 17, Saikat Panja Aug 01, Atomic size increases when moving down in a group thus electronegativity decreases when we move from top to bottom in the periodic table.

Metallic character decreases as you move across a period in the periodic table from left to right. This occurs as atoms more readily accept electrons to fill a valence shell than lose them to remove the unfilled shell. The valence electrons refer to the number of electrons in the outer shell. Across a period horizontal row , the valence electron increases. Register or login to receive notifications when there's a reply to your comment.

Don't want to keep filling in name and email whenever you want to comment? Register or login to make commenting easier. Save my name, email, and website in this browser for the next time I comment. Toggle navigation. Search Log In. Which of the following statements is correct about the periodic table?