Conditional if statement in python

Question

Instead of writing long 'if' statement, I would like to store that in some variable then pass it into 'if' condition. For example:

tempvar = '1 >0 and 10 > 12'
if tempvar:
 print something
else:
 do something

Does it possible in python ?

Thanks for your suggestion but my problem is something else which I can't figure out. I am doing multi string search in text file and trying to convert multi string into one condition:

 allspeciesfileter=['Homo sapiens', 'Mus musculus', 'Rattus norvegicus' ,'Sus scrofa']
 multiequerylist=[]
 if len(userprotein)> 0:
 multiequerylist.append("(str("+ "'"+userprotein+ "'"+")).lower() in (info[2].strip()).lower()")
 if len(useruniprotkb) >0:
 multiequerylist.append("(str("+ "'"+useruniprotkb+ "'"+")).lower() in (info[3].strip()).lower()")
 if len(userpepid) >0:
 multiequerylist.append("(str("+ "'"+userpepid+ "'"+")).lower() in (info[0].strip()).lower()")
 if len(userpepseq) >0:
 multiequerylist.append("(str("+ "'"+userpepseq+ "'"+")).lower() in (info[1].strip()).lower()")
 multiequery =' and '.join(multiequerylist)
 for line in pepfile:
 data=line.strip()
 info= data.split('\t')
 tempvar = bool (multiquery)
 if tempvar:
 do something

But that multiquery is not working

• Dan Mašek: The result of the expression (1 > 0) and (10 > 12) is a boolean value, so just store that in a variable. I.e. you're almost there, just don't turn the expression into a string (for whatever reason you did that).
• Paul85: Thanks for suggestion and I didn't know if condition use boolean

Answer 1

Just drop the string and store the condition in the variable.

>>> condition = 1 > 0 and 10 > 12
>>> if condition:
... print("condition is true")
... else:
... print("condition is false")
...
condition is false

You can even store a more complex condition with (for example) lambda

Here's random example using lambda with something a little more complex

(although using BS for parsing this is a bit overkill)

>>> from bs4 import BeautifulSoup
>>> html = "<a href='#' class='a-bad-class another-class another-class-again'>a link</a>"
>>> bad_classes = ['a-bad-class', 'another-bad-class']
>>> condition = lambda x: not any(c in bad_classes for c in x['class'])
>>> soup = BeautifulSoup(html, "html.parser")
>>> anchor = soup.find("a")
>>> if anchor.has_attr('class') and condition(anchor):
... print("No bad classes")
... else:
... print("Condition failed")
Condition failed

• Paul85: Thanks and it is really awesome. But I have updated my problem in details and this solution still not working for my case

Answer 2

I would highly recommend avoiding this in production code, due to performance, security and maintenance issues, but you can use eval to convert your strings to an actual bool value:

string_expression = '1 >0 and 10 > 12'
condition = eval(string_expression)
if condition:
 print something
else:
 do something

Answer 3

>>> 1 > 0 and 10 > 12
False
>>> '1 > 0 and 10 > 12'
'1 > 0 and 10 > 12'
>>> stringtest = '1 > 0 and 10 > 12'
>>> print(stringtest)
1 > 0 and 10 > 12
>>> if stringtest:
... print("OK")
... 
OK
>>> 1 > 0 and 10 < 12
True
>>> booleantest = 1 > 0 and 10 < 12
>>> print(booleantest)
True
>>>

The string type is True. You should drop the single quotes.