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Function annotation with two or more return parameters

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15

2

When I write an annotation for a function which returns one parameter, I have no problems.

def func() -> str:
 return "ok"

However, when I write an annotation with two or more parameters, my PyCharm gives me SyntaxError: invalid syntax.

def func() -> str, str:
 return "ok - 1", "ok - 2"

I think that the parameters can be combined with a tuple, but I don't think that's the best way to do it.

My question is: how can I properly annotate a function with two or more return parameters?

Please include a PEP link, if any, in your response. I looked for the answer at PEP 484 and PEP 3107 and could not find it.

python python-3.x type-hinting

share|improve this question

edited May 7 at 2:47

gmds

10.9k11038

asked May 7 at 2:05

KirillKirill

1809

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  It should be noted that the second func is equivalent to tmp = ('ok - 1', 'ok - 2') return tmp, making it immediately apparent why it requires Tuple.
  
  – Peilonrayz
  May 7 at 9:01
  

  
  
  
  

add a comment | 

15

2

When I write an annotation for a function which returns one parameter, I have no problems.

def func() -> str:
 return "ok"

However, when I write an annotation with two or more parameters, my PyCharm gives me SyntaxError: invalid syntax.

def func() -> str, str:
 return "ok - 1", "ok - 2"

I think that the parameters can be combined with a tuple, but I don't think that's the best way to do it.

My question is: how can I properly annotate a function with two or more return parameters?

Please include a PEP link, if any, in your response. I looked for the answer at PEP 484 and PEP 3107 and could not find it.

python python-3.x type-hinting

share|improve this question

edited May 7 at 2:47

gmds

10.9k11038

asked May 7 at 2:05

KirillKirill

1809

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  It should be noted that the second func is equivalent to tmp = ('ok - 1', 'ok - 2') return tmp, making it immediately apparent why it requires Tuple.
  
  – Peilonrayz
  May 7 at 9:01
  

  
  
  
  

add a comment | 

When I write an annotation for a function which returns one parameter, I have no problems.

def func() -> str:
 return "ok"

However, when I write an annotation with two or more parameters, my PyCharm gives me SyntaxError: invalid syntax.

def func() -> str, str:
 return "ok - 1", "ok - 2"

I think that the parameters can be combined with a tuple, but I don't think that's the best way to do it.

My question is: how can I properly annotate a function with two or more return parameters?

Please include a PEP link, if any, in your response. I looked for the answer at PEP 484 and PEP 3107 and could not find it.

python python-3.x type-hinting

share|improve this question

edited May 7 at 2:47

gmds

10.9k11038

asked May 7 at 2:05

KirillKirill

1809

def func() -> str:
 return "ok"

def func() -> str, str:
 return "ok - 1", "ok - 2"

share|improve this question

edited May 7 at 2:47

gmds

10.9k11038

asked May 7 at 2:05

KirillKirill

1809

share|improve this question

edited May 7 at 2:47

gmds

10.9k11038

asked May 7 at 2:05

KirillKirill

1809

edited May 7 at 2:47

gmds

10.9k11038

edited May 7 at 2:47

gmds

10.9k11038

asked May 7 at 2:05

KirillKirill

1809

asked May 7 at 2:05

KirillKirill

1809

1 Answer
1

active

oldest

votes

23

Use typing.Tuple:

from typing import Tuple

def func() -> Tuple[str, str]:
 return 'a', 'b'

This is appropriate because, conceptually, you are actually returning a single tuple containing those values. Note:

print(type(func()))

Output:

<class 'tuple'>

Note that except for the empty tuple (()), parentheses are not necessary to define a tuple, which means that 'a', 'b' is created as a tuple, rather than being separate values gathered into one by the return statement.

share|improve this answer

edited 2 hours ago

answered May 7 at 2:07

gmdsgmds

10.9k11038

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  Tuple is reasonable. It may be too strict in some cases, but there isn’t a better alternative without different tradeoffs as far as I can tell.
  
  – kojiro
  May 7 at 2:48
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @kojiro It seems to me that that would not apply in the case of return values...?
  
  – gmds
  May 7 at 2:50
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  I think it still applies. The main thing about the signature isn’t that the function returns a tuple per se, but that it return an unpackable with a specific length. There are plenty of sequence types that are unpackable, but no generic unpackable type that also has length and inner-type specifiers. Tuple can specify everything, but is too strict.
  
  – kojiro
  May 7 at 2:54
  
  

  
  
  
  


• 
  
  
  

  
  4
  

  
  
  
  
  
  

  
  
  @kojiro I might be misunderstanding you, but is it not the case that functions with multiple return values specifically return tuple, as opposed to a function with a single return value that also happens to be an unpackable object that knows its length and elements' types, which would require such a specifier?
  
  – gmds
  May 7 at 2:57
  
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  A tuple is still a single object that happens to be unpackable. That’s what I’m saying. There isn’t a way to express python returning multiple values from a function because python can’t return multiple values from a function. But it can return a sequence, and a tuple is one kind of sequence.
  
  – kojiro
  May 7 at 3:05
  

  
  
  
  

 | 
show 2 more comments

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23

Use typing.Tuple:

from typing import Tuple

def func() -> Tuple[str, str]:
 return 'a', 'b'

This is appropriate because, conceptually, you are actually returning a single tuple containing those values. Note:

print(type(func()))

Output:

<class 'tuple'>

Note that except for the empty tuple (()), parentheses are not necessary to define a tuple, which means that 'a', 'b' is created as a tuple, rather than being separate values gathered into one by the return statement.

share|improve this answer

edited 2 hours ago

answered May 7 at 2:07

gmdsgmds

10.9k11038

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  Tuple is reasonable. It may be too strict in some cases, but there isn’t a better alternative without different tradeoffs as far as I can tell.
  
  – kojiro
  May 7 at 2:48
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @kojiro It seems to me that that would not apply in the case of return values...?
  
  – gmds
  May 7 at 2:50
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  I think it still applies. The main thing about the signature isn’t that the function returns a tuple per se, but that it return an unpackable with a specific length. There are plenty of sequence types that are unpackable, but no generic unpackable type that also has length and inner-type specifiers. Tuple can specify everything, but is too strict.
  
  – kojiro
  May 7 at 2:54
  
  

  
  
  
  


• 
  
  
  

  
  4
  

  
  
  
  
  
  

  
  
  @kojiro I might be misunderstanding you, but is it not the case that functions with multiple return values specifically return tuple, as opposed to a function with a single return value that also happens to be an unpackable object that knows its length and elements' types, which would require such a specifier?
  
  – gmds
  May 7 at 2:57
  
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  A tuple is still a single object that happens to be unpackable. That’s what I’m saying. There isn’t a way to express python returning multiple values from a function because python can’t return multiple values from a function. But it can return a sequence, and a tuple is one kind of sequence.
  
  – kojiro
  May 7 at 3:05
  

  
  
  
  

 | 
show 2 more comments

23

Use typing.Tuple:

from typing import Tuple

def func() -> Tuple[str, str]:
 return 'a', 'b'

This is appropriate because, conceptually, you are actually returning a single tuple containing those values. Note:

print(type(func()))

Output:

<class 'tuple'>

Note that except for the empty tuple (()), parentheses are not necessary to define a tuple, which means that 'a', 'b' is created as a tuple, rather than being separate values gathered into one by the return statement.

share|improve this answer

edited 2 hours ago

answered May 7 at 2:07

gmdsgmds

10.9k11038

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  Tuple is reasonable. It may be too strict in some cases, but there isn’t a better alternative without different tradeoffs as far as I can tell.
  
  – kojiro
  May 7 at 2:48
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @kojiro It seems to me that that would not apply in the case of return values...?
  
  – gmds
  May 7 at 2:50
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  I think it still applies. The main thing about the signature isn’t that the function returns a tuple per se, but that it return an unpackable with a specific length. There are plenty of sequence types that are unpackable, but no generic unpackable type that also has length and inner-type specifiers. Tuple can specify everything, but is too strict.
  
  – kojiro
  May 7 at 2:54
  
  

  
  
  
  


• 
  
  
  

  
  4
  

  
  
  
  
  
  

  
  
  @kojiro I might be misunderstanding you, but is it not the case that functions with multiple return values specifically return tuple, as opposed to a function with a single return value that also happens to be an unpackable object that knows its length and elements' types, which would require such a specifier?
  
  – gmds
  May 7 at 2:57
  
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  A tuple is still a single object that happens to be unpackable. That’s what I’m saying. There isn’t a way to express python returning multiple values from a function because python can’t return multiple values from a function. But it can return a sequence, and a tuple is one kind of sequence.
  
  – kojiro
  May 7 at 3:05
  

  
  
  
  

 | 
show 2 more comments

Use typing.Tuple:

from typing import Tuple

def func() -> Tuple[str, str]:
 return 'a', 'b'

This is appropriate because, conceptually, you are actually returning a single tuple containing those values. Note:

print(type(func()))

Output:

<class 'tuple'>

Note that except for the empty tuple (()), parentheses are not necessary to define a tuple, which means that 'a', 'b' is created as a tuple, rather than being separate values gathered into one by the return statement.

share|improve this answer

edited 2 hours ago

answered May 7 at 2:07

gmdsgmds

10.9k11038

from typing import Tuple

def func() -> Tuple[str, str]:
 return 'a', 'b'

print(type(func()))

<class 'tuple'>

share|improve this answer

edited 2 hours ago

answered May 7 at 2:07

gmdsgmds

10.9k11038

answered May 7 at 2:07

gmdsgmds

10.9k11038

answered May 7 at 2:07

gmdsgmds

10.9k11038