def exchange(src, dst, amt):
"""
Returns the amount of currency received in the given exchange.
In this exchange, the user is changing amt money in currency src to the currency
dst. The value returned represents the amount in currency currency_to.
The value returned has type float.
Parameter src: the currency on hand
Precondition src is a string for a valid currency code
Parameter dst: the currency to convert to
Precondition dst is a string for a valid currency code
Parameter amt: amount of currency to convert
Precondition amt is a float or int
"""
assert type(src) == str and len(src) == 3, 'Precondition violation'
assert introcs.count_str(src, " ") == 0, 'Precondition violation'
assert type(dst) == str and len(dst) == 3, 'Precondition violation'
assert introcs.count_str(dst, " ") == 0, 'Precondition violation'
assert type(amt) == float or type(amt) == int, 'Precondition violation'
response = service_response(src, dst, amt)
idx = introcs.find_str(response, "dst")
convert_to = first_inside_quotes(response[idx + len("dst") + 1:])
amt_received = before_space(convert_to)
value = float(amt_received)
return value
def after_space(s):
"""
Returns the substring of s after the first space
Example: after_space('Hello World') returns 'World'
Parameter s: the string to slice
Precondition: s is a string with at least one space in it
"""
assert introcs.count_str(s, " ") != 0, 'Precondition violation'
idx = introcs.find_str(s, ' ')
sub = s[idx + 1:]
return sub
def service_response(src, dst, amt):
"""
Returns a JSON string that is a response to a currency query.
A currency query converts amt money in currency src to the currency dst. The response
should be a string of the form
'{"success": true, "src": "<src-amount>", dst: "<dst-amount>", error: ""}'
where the values src-amount and dst-amount contain the value and name for the src
and dst currencies, respectively. If the query is invalid, both src-amount and
dst-amount will be empty, and the error message will not be empty.
There may or may not be spaces after the colon. To test this function, you should
chose specific examples from your web browser.
Parameter src: the currency on hand
Precondition src is a nonempty string with only letters
Parameter dst: the currency to convert to
Precondition dst is a nonempty string with only letters
Parameter amt: amount of currency to convert
Precondition amt is a float or int
"""
assert type(src) == str and len(src) == 3, 'Precondition violation'
assert introcs.count_str(src, " ") == 0, 'Precondition violation'
assert type(dst) == str and len(dst) == 3, 'Precondition violation'
assert introcs.count_str(dst, " ") == 0, 'Precondition violation'
assert type(amt) == float or type(amt) == int, 'Precondition violation'
url = 'https://ecpyfac.ecornell.com/python/currency/fixed?src=' + src + '&dst='
url += dst + '&amt=' + str(amt) + '&key=' + APIKEY
json = introcs.urlread(url)
return json
def before_space(s):
"""
Returns the substring of s up to, but not including, the first space.
Example: before_space('Hello World') returns 'Hello'
Parameter s: the string to slice
Precondition: s is a string with at least one space in it
"""
assert introcs.count_str(s, " ") != 0, 'Precondition violation'
idx = introcs.find_str(s, ' ')
sub = s[:idx]
return sub
def first_inside_quotes(s):
"""
Returns the first substring of s between two (double) quote characters
Note that the double quotes must be part of the string. So "Hello World" is a
precondition violation, since there are no double quotes inside the string.
Example: first_inside_quotes('A "B C" D') returns 'B C'
Example: first_inside_quotes('A "B C" D "E F" G') returns 'B C', because it only
picks the first such substring.
Parameter s: a string to search
Precondition: s is a string with at least two (double) quote characters inside
"""
assert introcs.count_str(s, '"') >= 2, 'Precondition violation'
idx1 = introcs.index_str(s, '"')
idx2 = introcs.index_str(s, '"', idx1 + 1, len(s))
sub = s[(idx1 + 1):idx2]
return sub