a is actually slightly smaller than 1.555 due to imprecise representation of floating point values.

You can see this, for example, as follows:

f"{a:.40f}"
'1.5549999999999999378275106209912337362766'

Or,

f"{a:.64f}"
'1.5549999999999999378275106209912337362766265869140625000000000000'

It does work. You were just not assigning the format to a variable, and then just printing the original string. See example below:

>>> s = 'hello, {person}'
>>> s
'hello, {person}'
>>> s.format(person='james')
'hello, james'                    # your format works
>>> print s                       # but you did not assign it
hello, {person}                   # original `s`
>>> x = s.format(person='james')  # now assign it
>>> print x 
hello, james                      # works!

What's performed by your snippet is binary arithmetic operation, and it require single object as second argument.

With parenthesis, you defining this argument as a two-element tuple. I added additional parenthesis to emphasise how code is interpreted.

print ("My age is %d & my name is %s, what are you ?" % (my_age, my_name))

When not, argument is single element and , %my_name is interpreted as second argument to print statement.

print evaluates each expression in turn and writes the resulting object to standard output

print ("My age is %d & my name is %s, what are you ?" % my_age), (%my_name)

Since %my_name is invalid Python expression, SyntaxError is raised.

The problem here is that the format method is only being called for the final string in the 3 strings being added together. You should either apply the format operation AFTER you have concatenated the strings, or use a single string format that accepts line breaks (so you don't have to concatenate strings in the first place).

To apply after concatenation, you can just use an extra set of parentheses around the string concatenation, e.g.

 print(("Here are three other numbers." + \
" First number is {0:d}, second number is {1:d}, \n" + \
"third number is {2:d}") .format(7,8,9))

Or you can use triple quotes to accept line breaks, e.g.

print("""Here are three other numbers.\
First number is {0:d}, second number is {1:d},
third number is {2:d}""" .format(7,8,9))

where \ allows a line break in the code that wont be printed.

Python 3.2 does this correctly:

$ python3.2
Python 3.2.2 (default, Sep  5 2011, 22:09:30) 
[GCC 4.6.1] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> sqlstring = 'INSERT INTO {}'
>>> table = 'Product'
>>> sqlstring.format(table)
'INSERT INTO Product'
>>> 

What version are you using?

Additional thought:

Strings are immutable and do not self-modify in-place. Maybe you want:

sqlstring = sqlstring.format(table)

If format strings self-modified themselves in place it would be quite annoying for Python programmers, as each format string could only be used once. Sometimes we want the chance to build a nice format string then use it hundreds of times — which is easy if format() returns the result instead of modifying the format in-place.

You are missing the formatter type:

%(other_id)s

Note the s after the parenthesis; you want to interpolate the values as strings. Here is a working version instead:

jQuery = ("$('#%(other_id)s').click(function() { "
                  "    if ($(this).is(':checked')) { "
                  "        $('#%(text_id)s').show()     "
                  "    } "
                  "    else {"
                  "       $('#%(text_id)s').hide()"
                  "    }"
                  " });")

Dollar symbols have no meaning in %-style string formats and I've added the # id selectors for you. :-)

Personally, I would use """ triple-quotes instead:

jQuery = """\
$('#%{other_id}s').click(function() {
    if ($(this).is(':checked')) {
        $('#%(text_id)s').show()
    }
    else {
        $('#%(text_id)s').hide()
    }
});
"""

Better still, put this into a Jinja template anyway (since you are using Flask) and render that instead:

jquery = render_template('toggle_field.js', other_id=choice_id, text_id=text_choice_id)

where toggle_field.js is the Jinja template version of the jQuery snippet:

$('#{{ other_id }}').click(function() {
    if ($(this).is(':checked')) {
        $('#{{ text_id }}').show()
    }
    else {
        $('#{{ text_id }}').hide()
    }
});

You should escape literal braces by doubling them:

json_data_resp = '{{"error":false,"code":"{0}","mac":"{1}","message":"Device configured successfully"}}'.format(activation_code, macaddress)

Excerpt from Format String Syntax:

Format strings contain “replacement fields” surrounded by curly braces {}. Anything that is not contained in braces is considered literal text, which is copied unchanged to the output. If you need to include a brace character in the literal text, it can be escaped by doubling: {{ and }}.