Question

Following is the code block that is working as expected.

   for key in context:
        if isinstance(context[key],collections.Iterable):
            queryString += '%s=%s&' % (key, urllib.quote(context[key]))
        else:
            queryString += '%s=%s&' % (key, context[key])
    return queryString

But I did not understand the use of if block. Shouldn’t the following work?

for key in context:
    queryString += '%s=%s&' % (key, context[key])
return queryString

Answer 1

It is basically saying “quote anything that isn’t numeric or a sequence when converting to a string representation”. It escapes characters to make them urlencoded.

The if will prevent it from quoting int, float, etc, because those would crash the quote function.

context = {'a': 'a b c', 'b': ('a', '@', 'c'), 'c': 1}
queryString = ''

for key in context:
    if isinstance(context[key],collections.Iterable):
        queryString += '%s=%s&' % (key, urllib.quote(context[key]))
    else:
        queryString += '%s=%s&' % (key, context[key])

print queryString
# a=a%20b%20c&c=1&b=a%40c&

Though it only makes sense depending on what your potential inputs could be (the value of context). It would crash on say, a list of ints.

Not using quote would look like this:

for key in context:
    queryString += '%s=%s&' % (key, context[key])

# invalid url format
# a=a b c&c=1&b=('a', '@', 'c')&

And running the quote on everything would result in:

for key in context:
    queryString += '%s=%s&' % (key, urllib.quote(context[key]))
...
TypeError: argument 2 to map() must support iteration