python check if values exist in list

Question

couldn't get this correct. I want to check the contents of the list for a set of values. I should not be falling inside the conditional if because the value doesn't exist.

Following list contains: ['pm_pmdo', 'pm_pmco', 'shv', 'dsv', 'pmv']

Checking for the following: she, dse, pme

inside found one?

class newfunc(object): def testfunction(self): self.DSE = 'dse' self.PME = 'pme' self.SHE = 'she' self.users_roles = ['pm_pmdo', 'pm_pmco', 'shv', 'dsv', 'pmv'] print 'Following list contains:' print self.users_roles print 'Checking for the following:' print self.SHE print self.DSE print self.PME if (self.DSE or self.PME or self.SHE for s in self.users_roles): #if (self.DSE or self.PME or self.SHE) in self.users_roles: print "inside found one" else: print "outside none found" if __name__ == '__main__': runtime = newfunc() runtime.testfunction()

kindall · Accepted Answer · 2015-03-27 20:53:37Z

2

if any(role in self.users_roles for role in (self.SHE, self.PME, self.SHE)):

answered Mar 27, 2015 at 20:53

kindall

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Comments

martineau · Accepted Answer · 2015-03-27 21:52:35Z

sets are good containers for quick membership testing if order doesn't matter:

class NewFunc(object): def testfunction(self): self.DSE = 'dse' self.PME = 'pme' self.SHE = 'she' self.users_roles = {'pm_pmdo', 'pm_pmco', 'shv', 'dsv', 'pmv'} print 'users_roles:' print list(self.users_roles) print 'Checking for the following:' print self.SHE print self.DSE print self.PME if {self.DSE, self.PME, self.SHE} & self.users_roles: print "found at least one" else: print "none found" if __name__ == '__main__': runtime = NewFunc() runtime.testfunction()

Padraic Cunningham · Accepted Answer · 2015-03-27 21:21:06Z

Use any which short circuits returning True if we do find a match or evaluates to False otherwise:

if any(s in self.users_roles for s in (self.DSE , self.PME , self.SHE ))

Your code always evaluates to True as if self.DSE is basically checking if bool(self.DSE) which will always evaluate to True for any non empty string, it is the same for self.PME and self.SHE.

In [21]: bool("foo") # will be the same for all non empty strings Out[21]: True In [22]: bool("") Out[22]: False

You can also make self.users_roles a set and use set.intersection:

self.users_roles = {'pm_pmdo', 'pm_pmco', 'shv', 'dsv', 'pmv'} if self.users_roles.intersection([self.DSE, self.PME, self.SHE])

Ouch.. So something like this would also be a big no no? if self.PME has a vailue then - if (self.PME) in self.users_roles: Thanks!
@DaveJones, unless you always want the if to evaluate to True for every non empty string possible then yes it is a big no no ;) The only way it would ever be False if if you got pass empty strings. If you are doing a lot of checks the set will be much more efficient than using any. The correct way to write it would be if self.DSE in self.users_roles or self.PME in self.users_roles etc... but that gets pretty ugly when you have a few to check so any is just a more concise way to do it.

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