I've been searching for my problem here, but i can't find the exact answer to my problem.
I call a sympy function ( solve() ). This function can return a full list or an empty list.
I call this piece of code inside a while:
try:
sol = solve([eq1,eq2],[r,s])
rB = bin(abs(sol[0][0]))
sB = bin(abs(sol[0][1]))
stop = True
r = rB[2:len(rB)]
s = sB[2:len(sB)]
P = int("0b"+r+s,2)
Q = int("0b"+s+r,2)
print(P*Q == pubKey.n)
print("P = {}".format(P))
print("Q = {}".format(Q))
break
except ValueError:
pass
What i want is:
if the solve() returns an empty list, just pass. And if the solve() returns a full list, keep with the execution. The solve will be returning empty list until i find the right value.
This can be reached by checking sol[0][0], if there's a non-empty list this will work, but if the list is empty, this will throw an error (null pointer) i want try to flag it and pass.
What i'm having now is that when sol is empty, it tries to get sol[0][0], and ofc this throws an error that's not being catched by the try, and the whole code stops.
Anyone knows a solution for that? I'm not using try correctly?
Set sol in the beginning of each loop to some value and check it in the except clause
about else
try/except has an else which will be run the try block did not raise an Exception
and for has an else clause for when it was not broken out of!
for foo in iterable:
# set value so the name will be available
# can be set prior to the loop, but this clears it on each iteration
# which seems more desirable for your case
sol = None
try:
"logic here"
except Exception:
if isinstance(sol, list):
"case where sol is a list and not None"
# pass is implied
else: # did not raise an Exception
break
else: # did not break out of for loop
raise Exception("for loop was not broken out of!")
Related
I have below code block:
try:
if str(symbol.args[0]) != str(expr.args[0]):
print('true')
raise SyntaxError('====error')
except:
pass
Here I am trying to raise Syntax error if certain condition is true.I am testing this code block, I can see 'true' is getting printed which means condition is met but even after that also the code is not throwing syntax error.
I am trying to understand what is wrong in the above code.
You're putting pass in the except: block which is swallowing the exception. Either remove the code from the try-except block or change pass to raise
Above answer is pointing the issue, I just want to give some examples to help you better understand how try/except works:
# Just raise an exception (no try/except is needed)
if 1 != 2:
raise ValueError("Values do not match")
# Catch an exception and handle it
a = "1"
b = 2
try:
a += b
except TypeError:
print("Cannot add an int to a str")
# Catch an exception, do something about it and re-raise it
a = "1"
b = 2
try:
a += b
except TypeError:
print("Got to add an int to a str. I'm re-raising the exception")
raise
try/except can also be followed by else and finally, you can check more about these here: try-except-else-finally
Was experimenting with applying memoization decorator to recursive functions using standard python #decorator notation, which worked beautifully. According to much of the documentation I've read, these code examples are supposed to be equivalent:
# letting python decorator mechanism take care of wrapping your function with the decorator function
#decorator
def func(): . . .
print(func(arg))
AND
# manually wrapping the decorator function around the function
func = decorator(func)
print(func(arg))
When I do this, however, I get an UnboundLocalError on func.
If I change the code to
new_name = decorator(func)
print(new_name(func))
The code runs, but the decorator is only applied to the first call and not to any of the recursive calls (this did NOT surprise me), but I don't get any error messages either.
What seems weird to me, however, is the original error message itself.
If I experiment further and try the following code:
new_name = decorator(func)
func = new_name
print(func(arg))
I get the same error ON THE SAME LINE AS BEFORE (????)
In fact, if I form a chain of these assignments, with func = several_names_later
I still get the same error on the ORIGINAL line
Can anyone explain what is going on, and why I'm getting the error, and why it seems that the error is disconnected from the location of the variable in question?
As requested, here is most of the actual code (with just one of the recursive functions), hope it's not too much . . .
import functools
def memoize(fn):
cache = dict()
#functools.wraps(fn)
def memoizer(*args):
print(args)
if args not in cache:
cache[args] = fn(*args)
return cache[args]
return memoizer
##memoize
def number_sum(n):
'''Returns the sum of the first n numbers'''
assert(n >= 0), 'n must be >= 0'
if n == 0:
return 0
else:
return n + number_sum(n-1)
def main():
# Book I'm reading claims this can be done but I get error instead:
number_sum = memoize(number_sum) # this is the flagged line
print(number_sum(300))
#UnboundLocalError: local variable 'number_sum' referenced before assignment
# When I do this instead, only applies decorator to first call, as I suspected
# but works otherwise: no errors and correct - but slow - results
# No complaints about number_sum
wrapped_number_sum = memoize(number_sum)
print(wrapped_number_sum(300))
# This is what is odd:
# When I do any version of this, I get the same error as above, but always on
# the original line, flagging number_sum as the problem
wrapped_number_sum = memoize(number_sum) # the flagged line, no matter what
number_sum = wrapped_number_sum
print(number_sum(300))
OR even:
wrapped_number_sum = memoize(number_sum) # still the flagged line
another_variable = wrapped_number_sum
number_sum = another_variable
print(number_sum(300))
if __name__ == '__main__':
main()
I am more than a little mystified at this.
I want to verify if Items from a List are contained in what i fetch by using string.read().
How do I do this:
if string.find(lisst):
do_whatever()
elif string.find(lisst2):
do_something_else()
Example is pretty basic, but that's all I want to do. I keep getting invalid syntax error. :(
def verify(text):
lisst = ['awesome','failed','trolling']
lisst2 = ['boring','bad']
s = requests.get(text)
t = s.read()
if t.find(lisst):
print("Someone was awesome, failing or trolling!")
elif t.find(lisst2)
print("Something retarded happened")
error is thrown at elif t.find(lisst2), so I need a workaround.
elif any(n in t for n in lisst2):
^
SyntaxError: invalid syntax
Thank you in advance!
If I understood correctly, you want to do something in an if block if a string contains any the elements of a list.
if any(str in aVeryLongStringData for str in myList):
doStuff()
If you want to check if your data contains all of the elements on your list, you can just change "any" to "all"
if all(str in aVeryLongStringData for str in myList):
doStuff()
I created a loop (while True) to automate a task on the site with python. This code clicks on two fields until an element appears on the page
(browser.find_element_by_id ('formComp: buttonBack').
When this element appears, I want the loop to stop and go to the next block of code.
I tested it that way, but it made a mistake. Python reported that the element "formComp: buttonback" was not found. But that's just it, if not found continue the loop:
while (browser.find_element_by_id('formComp:repeatCompromissoLista:0:tableRealizacao:0:subtableVinculacoes:0:vinculacao_input')):
vinc = wait.until(EC.presence_of_element_located((By.ID, 'formComp:repeatCompromissoLista:0:tableRealizacao:0:subtableVinculacoes:0:vinculacao_input')))
vinc = browser.find_element_by_id('formComp:repeatCompromissoLista:0:tableRealizacao:0:subtableVinculacoes:0:vinculacao_input')
vinc.send_keys('400')
enterElem5 = wait.until(EC.element_to_be_clickable((By.ID, 'formComp:buttonConfirmar')))
enterElem5 = browser.find_element_by_id('formComp:buttonConfirmar')
enterElem5.send_keys(Keys.ENTER)
time.sleep(int(segundosv))
if (browser.find_element_by_id('formComp:buttonRetornar')== True):
break
else:
continue
Try like this hope this helps.Check the length count of the button more than 0.
if (len(browser.find_elements_by_id('formComp:buttonRetornar'))>0):
break
else:
continue
find_element_by_id() does not return False when an element is not found. Instead, it raises selenium.common.exceptions.NoSuchElementException. You can handle the exception to get the flow control you are looking for:
try:
browser.find_element_by_id('formComp:buttonRetornar')
break
except NoSuchElementException:
continue
While this is a project assignment for class I am trying to understand how to do a specific part of the project.
I need to go through an html file and check if all the opening statements are matched to closing statements. Further, they must be in the correct order and this must be checked using a stack I've implemented. As of right now I am working on extracting each tag from the file. The tough part seems to be the two exceptions that I am working on here. The and the . I need these tags to be removed so the program doesn't read them as an opening or closing statement.
class Stack(object):
def __init__(self):
self.items = []
def isEmpty(self):
return self.items = []
def push(self, item):
self.items.append(item)
def pop(self):
return self.items[-1]
def getTag(file):
EXCEPTIONS = ['br/', 'meta']
s = Stack()
balanced = True
i = 0
isCopying = False
currentTag = ''
isClosing = False
while i < len(file) and balanced:
if symbol == "<":
if i < (len(file) - 1) and file[i + 1] == "/":
i = i + 1
isClosing == True
isCopying == True
if symbol == ">":
if isClosing == True:
top = s.pop()
if not matches(top, symbol):
balanced = False
else:
**strong text**
s.push(currentTag)
currentTag = ''
isCopying == False
if isCopying == True:
currentTag += symbol
The code reads in the file and goes letter by letter to search for <string>. If it exists it pushes it on to the stack. The matches functions checks to see if the closing statement equals the opening statement. The exceptions list is the ones I have to check for that will screw up the placing of the strings on the stack. I am having a tough time trying to incorporate them into my code. Any ideas? Before I push on to the stack I should go through a filter system to see whether that statement is valid or not valid. A basic if statement should suffice.
If I read your requirements correctly, you're going about this very awkwardly. What you're really looking to do is tokenize your file, and so the first thing you should do is get all the tokens in your file, and then check to see if it is a valid ordering of tokens.
Tokenization means you parse through your file and find all valid tokens and put them in an ordered list. A valid token in your case is any string length that starts with a < and ends with a >. You can safely discard the rest of the information I think? It would be easiest if you had a Token class to contain your token types.
Once you have that ordered list of tokens it is much easier to determine if they are a 'correct ordering' using your stack:
is_correct_ordering algorithm:
For each element in the list
if the element is an open-token, put it on the stack
if the element is a close-token
if the stack is empty return false
if the top element of the stack is a matching close token
pop the top element of the stack
else return false
discard any other token
If the stack is NOT empty, return false
Else return true
Naturally, having a reasonable Token class structure makes things easy:
class Token:
def matches(t: Token) -> bool:
pass # TODO Implement
#classmethod
def tokenize(token_string: str) -> Token:
pass # TODO Implement to return the proper subclass instantiation of the given string
class OpenToken:
pass
class CloseToken:
pass
class OtherToken:
pass
This breaks the challenge into two parts: first parsing the file for all valid tokens (easy to validate because you can hand-compare your ordered list with what you see in the file) and then validating that the ordered list is correct. Note that here, too, you can simplify what you're working on by delegating work to a sub-routine:
def tokenize_file(file) -> list:
token_list = []
while i < len(file):
token_string, token_end = get_token(file[i:])
token_list.append = Token.tokenize(token_string)
i = i + token_end # Skip to the end of this token
return token_list
def get_token(file) -> tuple:
# Note this is a naive implementation. Consider the edge case:
# <img src="Valid string with >">
token_string = ""
for x in range(len(file)):
token_string.append(file[x])
if file[x] == '>':
return token_string, x
# Note that this function will fail if the file terminates before you find a closing tag!
The above should turn something like this:
<html>Blah<meta src="lala"/><body><br/></body></html>
Into:
[OpenToken('<html>'),
OtherToken('<meta src="lala"/>'),
OpenToken('<body>'),
OtherToken('<br/>'),
CloseToken('</body>'),
CloseToken('</html>')]
Which can be much more easily handled to determine correctness.
Obviously this isn't a complete implementation of your problem, but hopefully it will help straighten out the awkwardness you've chosen with your current direction.