Tuple passed to function recognised as string

[Mike314]

Hello,

I have following code:

def test_func(val):
print type(val)

test_func(val=('val1'))
test_func(val=('val1', 'val2'))

The output is quite different:

<type 'str'>
<type 'tuple'>

Why I have string in the first case?

Thanks.

 

[MRAB]

Hello,

I have following code:

def test_func(val):
print type(val)

test_func(val=('val1'))
test_func(val=('val1', 'val2'))

The output is quite different:

<type 'str'>
<type 'tuple'>

Why I have string in the first case?

It's the comma that makes the tuple, except for one special case: the
empty tuple "()". The parentheses are there just for clarity and
operator precedence.

('val1') is not a 1-tuple, but just parentheses for grouping. The
1-tuple is ('val1', ). Notice that a trailing comma is allowed in tuples
as well as list and dict literals, eg (1, 2, ), [1, 2, ], {1: 2, 3: 4,
}.

 

[Terry Reedy]

Hello,

I have following code:

def test_func(val):
print type(val)

test_func(val=('val1'))
test_func(val=('val1', 'val2'))

The output is quite different:

<type 'str'>
<type 'tuple'>

Why I have string in the first case?

Because (<any expression>) == <any expression>.
Perhaps you meant ('val1',).

"Parenthesized forms
A parenthesized form is an optional expression list enclosed in parentheses:

parenth_form ::= "(" [expression_list] ")"

A parenthesized expression list yields whatever that expression list
yields: if the list contains at least one comma, it yields a tuple;
otherwise, it yields the single expression that makes up the expression
list.

An empty pair of parentheses yields an empty tuple object.
"

 

[Albert Hopkins]

Hello,

I have following code:

def test_func(val):
print type(val)

test_func(val=('val1'))
test_func(val=('val1', 'val2'))

The output is quite different:

<type 'str'>
<type 'tuple'>

Why I have string in the first case?

You could have verified this simply by getting rid of the function
altogether:
--> <type 'str'>

Hint 1:--> <type 'int'>

Hint 2: It's not the parentheses that define a tuple, it's the comma(s)--> <type 'tuple'>

 

[R. David Murray]

Hello,

I have following code:

def test_func(val):
print type(val)

test_func(val=('val1'))
test_func(val=('val1', 'val2'))

The output is quite different:

<type 'str'>
<type 'tuple'>

Why I have string in the first case?

Because in Python the syntactic element that defines something
as a tuple is the comma, not the parenthesis:
<type 'tuple'>

In your function call the comma would normally be an argument
separator, so in that context you do need the parenthesis as well:

test_func(val=('val1',))