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> If casting from a string to a type works with ints and floats, why not with bools? What possible justification is there? There's no type casting in Python. i

> If casting from a string to a type works with ints and floats, why not with bools? What possible justification is there? There's no type casting in Python. int(), float() and bool() just create objects of their respective types, passing the arguments to the initializer. They are not fundamentally different from, say, PostgresqlDriver() in this regard. Different classes will provide different ways to construct objects depending on what is most useful. For int and float, the most useful thing to do when receiving a string is to parse it; for bool, the most useful thing to do is to check its truthiness; for PostgresqlDriver, the most useful thing to do is to interpret it as a database URL and connect to it.

crazygringo 1y ago
> There's no type casting in Python. If you search "type casting in Python" you will find lots of articles explaining how to use int(), str(), etc. to cast. This is a common and well-documented concept, even if it's different under the hood from e.g. C. The idea that you'd name a function bool() and have it act differently is a deeply confusing design decision that it's understandable people would get misled by and frustrated with. This is a function named after a fundamental type. It's not a random user-defined constructor.
- bb88 1y ago
  If we do it that way, we have worse problems. if "False": # What do you expect? True or False? print("True") else: print("False") bool() is consistent with how "truthiness" happens in python. Otherwise we end up with the YAML norway problem. if bool("False"): print("True") else: print("False") # This would be different if we landed here. And that would be different behavior then the above -- creating a nasty inconsistency. Honestly it's not that hard to write something that looks like this: def str_to_bool(val: str) -> bool: return val.lower() in ["yes", "true", "1"]
- jonathrg 1y ago
  bool() is not a function named after a fundamental type. bool is a type. As with any type, you can call bool(...) to construct a new object of that type. https://docs.python.org/3/library/functions.html#bool https://docs.python.org/3/library/functions.html#bool A good tutorial will reflect this fact and use appropriate language. Both the idea that you can "cast", and the idea that bool is a function, are misunderstandings rooted in the idea that Python should be like C in all ways.
tmh88j 1y ago
> There's no type casting in Python. int(), float() and bool() just create objects of their respective types, passing the arguments to the initializer int() and float() behave like type casting, bool() does not. It's a truthiness check that would be more aptly named istruthy(). In python non-empty strings are truthy, so providing any string except for "" to bool() will return True, including "False".
- shakna 1y ago
  It's not casting. (char*)21 != "21" Casting is converting the container, the interpretation. What you're reaching for is type conversion. Some languages have "implicit conversion" when casting, but the word itself doesn't require it.
  - tmh88j 1y ago
    Yep, that's why I said "behaves like".
  - kazinator 1y ago
    In C, cast converts a value to another type (or a more or less qualified version of the same type). What that conversion means depends on the source and destination type. A cast of insert a conversion that wouldn't take place: 1/2 vs 1/(double)2 or coerce a conversion that otherwise requires a diagnostic: bar *b = 0; foo *f = (foo *) b; Loosely speaking, casting is another name for coercion, which refers to making a conversion happen that might not otherwise.
    - shakna 1y ago
      Implicit conversion, which is what you're mostly referring to here, is not required. It happens in some languages, and not others. Because I'm tired, and this is a very basic topic, I'm afraid I'm just going to rip from Wikipedia: > In most ALGOL-like languages, such as Pascal, Modula-2, Ada and Delphi, conversion and casting are distinctly different concepts. In these languages, conversion refers to either implicitly or explicitly changing a value from one data type storage format to another, e.g. a 16-bit integer to a 32-bit integer. The storage needs may change as a result of the conversion, including a possible loss of precision or truncation. The word cast, on the other hand, refers to explicitly changing the interpretation of the bit pattern representing a value from one type to another. For example, 32 contiguous bits may be treated as an array of 32 Booleans, a 4-byte string, an unsigned 32-bit integer or an IEEE single precision floating point value. Because the stored bits are never changed, the programmer must know low level details such as representation format, byte order, and alignment needs, to meaningfully cast. > In the C family of languages and ALGOL 68, the word cast typically refers to an explicit type conversion (as opposed to an implicit conversion), causing some ambiguity about whether this is a re-interpretation of a bit-pattern or a real data representation conversion. More important is the multitude of ways and rules that apply to what data type (or class) is located by a pointer and how a pointer may be adjusted by the compiler in cases like object (class) inheritance.

crazygringo 1y ago

> There's no type casting in Python. If you search "type casting in Python" you will find lots of articles explaining how to use int(), str(), etc. to cast. This is a common and well-documented concept, even if it's different under the hood from e.g. C. The idea that you'd name a function bool() and have it act differently is a deeply confusing design decision that it's understandable people would get misled by and frustrated with. This is a function named after a fundamental type. It's not a random user-defined constructor.

bb88 1y ago
If we do it that way, we have worse problems. if "False": # What do you expect? True or False? print("True") else: print("False") bool() is consistent with how "truthiness" happens in python. Otherwise we end up with the YAML norway problem. if bool("False"): print("True") else: print("False") # This would be different if we landed here. And that would be different behavior then the above -- creating a nasty inconsistency. Honestly it's not that hard to write something that looks like this: def str_to_bool(val: str) -> bool: return val.lower() in ["yes", "true", "1"]
jonathrg 1y ago
bool() is not a function named after a fundamental type. bool is a type. As with any type, you can call bool(...) to construct a new object of that type. https://docs.python.org/3/library/functions.html#bool https://docs.python.org/3/library/functions.html#bool A good tutorial will reflect this fact and use appropriate language. Both the idea that you can "cast", and the idea that bool is a function, are misunderstandings rooted in the idea that Python should be like C in all ways.

tmh88j 1y ago

> There's no type casting in Python. int(), float() and bool() just create objects of their respective types, passing the arguments to the initializer int() and float() behave like type casting, bool() does not. It's a truthiness check that would be more aptly named istruthy(). In python non-empty strings are truthy, so providing any string except for "" to bool() will return True, including "False".

shakna 1y ago
It's not casting. (char*)21 != "21" Casting is converting the container, the interpretation. What you're reaching for is type conversion. Some languages have "implicit conversion" when casting, but the word itself doesn't require it.
- tmh88j 1y ago
  Yep, that's why I said "behaves like".
- kazinator 1y ago
  In C, cast converts a value to another type (or a more or less qualified version of the same type). What that conversion means depends on the source and destination type. A cast of insert a conversion that wouldn't take place: 1/2 vs 1/(double)2 or coerce a conversion that otherwise requires a diagnostic: bar *b = 0; foo *f = (foo *) b; Loosely speaking, casting is another name for coercion, which refers to making a conversion happen that might not otherwise.
  - shakna 1y ago
    Implicit conversion, which is what you're mostly referring to here, is not required. It happens in some languages, and not others. Because I'm tired, and this is a very basic topic, I'm afraid I'm just going to rip from Wikipedia: > In most ALGOL-like languages, such as Pascal, Modula-2, Ada and Delphi, conversion and casting are distinctly different concepts. In these languages, conversion refers to either implicitly or explicitly changing a value from one data type storage format to another, e.g. a 16-bit integer to a 32-bit integer. The storage needs may change as a result of the conversion, including a possible loss of precision or truncation. The word cast, on the other hand, refers to explicitly changing the interpretation of the bit pattern representing a value from one type to another. For example, 32 contiguous bits may be treated as an array of 32 Booleans, a 4-byte string, an unsigned 32-bit integer or an IEEE single precision floating point value. Because the stored bits are never changed, the programmer must know low level details such as representation format, byte order, and alignment needs, to meaningfully cast. > In the C family of languages and ALGOL 68, the word cast typically refers to an explicit type conversion (as opposed to an implicit conversion), causing some ambiguity about whether this is a re-interpretation of a bit-pattern or a real data representation conversion. More important is the multitude of ways and rules that apply to what data type (or class) is located by a pointer and how a pointer may be adjusted by the compiler in cases like object (class) inheritance.