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Why does argv include the program name? Browse other questions tagged python python-2.7 or ask your own question. Other approaches reduce the number of if statements, but not the number of executed if statements. There exists 2 quiz/question(s) for this tutorial.

safe_dict['abs'] = abs user_func = raw_input("type a function: y = ") for x in range(1,10): # add x in safe_dict['x']=x print "x = ", x , ", y = ", eval(user_func,{"__builtins__":None},safe_dict) Here is an example with the function $$g(t) = Ae^{-at}\sin (\omega x)$$: g = StringFunction('A*exp(-a*t)*sin(omega*x)', independent_variable='t', A=1, a=0.1, omega=pi, x=0.5) The first argument is the function formula, as before, The tool is named StringFunction and works as follows: >>> from scitools.StringFunction import StringFunction >>> formula = 'exp(x)*sin(x)' >>> f = StringFunction(formula) # turn formula into f(x) func. Much safer.

list_str = "[1,5,7,8,2]" list_str = eval(list_str) print(list_str) print(list_str[1]) First, we define a string, that carries the syntax of a list. The magic exec function Having presented eval for turning strings into Python code, we take the opportunity to also describe the related exec function to execute a string containing arbitrary Python If there are just a few they can be done fairly manually: print "x = ", x , ", y = ", eval(user_func,{"__builtins__":None},{"x":x,"sin":sin}) Now sin(x) will work again, however hidden_value will For example, you could build a list of tuples (condition, error message) like this: conditions = [(lambda: not placeToGo, "Enter a positive integer in the text box"), (lambda: int(placeToGo) <= 0,

What is the most expensive item I could buy with £50? How would a vagrant civilization evolve? "all empires will suffer the same fate should the lessons from history go unlearnt" How to solve the old 'gun on a spaceship' problem? more hot questions question feed lang-py about us tour help blog chat data legal privacy policy work here advertising info mobile contact us feedback Technology Life / Arts Culture / Recreation Create a new command that supports superscript (^) and subscript(_) syntax This riddle could be extremely useful Determine if a coin system is Canonical How do I help minimize interruptions during

You could simply catch the NameError (and SyntaxError as well) and assume the input was a string: try: print(eval(line)) except (NameError, SyntaxError): print(line) There may be other exceptions raised here, but If you're going to do OO, make the error-reporting class implement the behaviour - once - and have the checks be a class that contains the salient properties (the check to Next, we use eval to evaluate it.Finally, we can show that it has the properties of a Python list. A common question i see is something like "How do you convert a string of a list to a list?" Sometimes it gets more complicated, like a string of a list

You might notice that the __builtins__ functions still work (try abs(-1)). House of Santa Claus Which option did Harry Potter pick for the knight bus? History Date User Action Args 2007-08-2420:03:50georg.brandlsetstatus: open -> closednosy: + georg.brandlmessages: + msg55273resolution: not a bug 2007-08-2419:59:24Rayfwardcreate Website maintained by the Python community hosting by Upfront Systems / powered by Roundup Instead, parse the data manually. –Gareth Latty Jan 10 '13 at 12:41 add a comment| 3 Answers 3 active oldest votes up vote 5 down vote accepted First: It's rarely a

File "", line 0, in ? Then you just call each function in turn. An example may clarify the point. Here is an example where the string to be evaluated is '2.5', which causes Python to see r = 2.5 and make a float object: >>> r = eval('2.5') >>> r

Administration User List Committer List Help Tracker Documentation Tracker Development Report Tracker Problem Issue1013 classification Title: eval error Type: behavior Stage: Components: Versions: Python 2.5 process Status: closed Resolution: not a Because "fasdfasd" is seen as a variable. Browse other questions tagged python or ask your own question. In Lybniz a list of safe functions is made, and used to filter the existing namespace. #!/usr/bin/env python from math import * hidden_value = "this is secret" def dangerous_function(filename): print open(filename).read()

Applying eval to user input So, why is the eval function so useful? This issue is now closed. I'm creating a script that works just like a Brute-Force algorithm but it won't break passwords but find the solution to a special form of an equation (more details are unnecessary). Why did it take 10,000 years to discover the Bajoran wormhole?

A better technique would be to use ast.literal_eval instead: try: print(ast.literal_eval(line)) except ValueError: print(line) literal_eval only accept python literal values (so 'string' or 123 or ('some', 'more', [1, 2, 4.5], 'complex Physically locating the server more hot questions question feed lang-py about us tour help blog chat data legal privacy policy work here advertising info mobile contact us feedback Technology Life / Let's pass in an empty namespace:>>> print eval("__import__('os').remove('file')", {}) Traceback (innermost last): File "", line 1, in ? A list of checks is being applied; treating them as a list is more accurate, flexible and extensible (you can have a list of named functions, there is no need for

Don't use eval to create variables. The program code itself has no knowledge about the kind of function the user wants to work with, yet at run time the user's desired formula enters the computations. Is intelligence the "natural" product of evolution? I want to write a function which evaluates inputted values and prints the result.

Are "ŝati" and "plaĉi al" interchangeable? How to tell why macOS thinks that a certificate is revoked? Unusual keyboard in a picture Why are unsigned numbers implemented? You repeat that logic in each function... –itsbruce Jan 9 '14 at 9:04 1 ...

The next job is to fill the local name space with functions and variables that are needed. Consider a small program where we read in two values and add them. Messages (2) msg55272 - (view) Author: Ray Ward (Rayfward) Date: 2007-08-24 19:59 >>> eval("9") 9 Works but. >>> eval("09") Traceback (most recent call last): File "", line 1, in File How to make python ignore syntactical errors occurring in eval? (The program shouldn't terminate) python eval share|improve this question edited Jan 26 '10 at 16:09 SilentGhost 126k33220236 asked Jan 26 '10

The eval(formula) expression means eval('2*sin(x)+1'), and the corresponding statement result = eval(formula is therefore effectively result = 2*sin(x)+1, which requires sin and x to be defined objects. When we get input via raw_input or sys.argv, it is always in the form of a string object, which often must be converted to another type of object, usually an int except ValueError: ... search Home +=1 Store Community Log in Sign up Home +=1 Store Community Log in Sign up Eval Module with Python Tutorial The idea of eval is to evaluate an expression

The eval function can then be of help: we feed the string object from the input to the eval function and let the it interpret the string and convert it to more stack exchange communities company blog Stack Exchange Inbox Reputation and Badges sign up log in tour help Tour Start here for a quick overview of the site Help Center Detailed Why did it take 10,000 years to discover the Bajoran wormhole? Not the answer you're looking for?

You can see which functions and variables are available with the dir() function type a function: y = dir() x = 1 , y = ['__builtins__', '__doc__', '__file__', '__name__', 'acos', 'asin Applying eval to strings If we put a string, enclosed in quotes, inside the expression string, the result is a string object: >>> >>> r = eval('"math programming"') >>> r 'math Don't use eval if you cannot trust the source. How do I explain that this is a terrible idea?

share|improve this answer edited Jan 10 '13 at 12:44 answered Jan 10 '13 at 12:38 Martijn Pieters♦ 500k7412981454 Surely this will still explode for something like this as a How? Providing cos(x) as the first command-line argument creates a need to have cos defined, so that is why we import all functions from the math module. A sample run for $$\int_0^{\pi/2} \sin(x)dx$$ goes like integrate.py "sin(x)" 0 pi/2 integral of sin(x) on [0, 1.5708] with n=200: 1 (The quotes in "sin(x)" are needed because of

For example, this code wont work: eval("if True: print('yep!')") This should give you an invalid syntax error With that shown, all hope is not lost if you want to basically do