CODEWITHSUNDEEP
pythonif-statementdictionaryboolean
user2799714
user2799714

Reputation: 9

How is this 'if' statement being used?

Could someone help me understand how the 'if' statements are being used in this bit of code? This is an exercise from the LearnStreet series of Python lessons: http://www.learnstreet.com/lessons/study/python#get-hint

I thought 'if' statements required a Boolean condition: if X < Y, then do Z. But I don't see how Booleans are a part of these 'if' statements.

def run():
     smiths = {"father": "Mike", "ex-wife" : "Mary", "children" : ["Bobby", "Susan"] }
     jones = {"mother": "Lucy", "ex-husband": "Peter", "children": ["Michelle", "Jeff", "Evan"]}
     family = {}
     for key in smiths:
         if key in family:
             family[key]+=smiths[key]
         else:
             family[key]=smiths[key]
     for key in jones:
         if key in family:
             family[key]+=jones[key]
         else:
             family[key]=jones[key]
     keysToDel = []
     for key in family:
         if 'ex' in key:
             keysToDel.append(key)
     print keysToDel
     for key in keysToDel:
         del family[key]
     return family

Upvotes: 0

Views: 140

Answers (4)

Siva Cn
Siva Cn

Reputation: 947

if key in family:

Here the key is an element and the family is an container or sequence

and you are trying to find the existence of the key in the family

this if statement returns True if the key is found in the container otherwise returns False

Upvotes: 1

BartoszKP
BartoszKP

Reputation: 35901

These are boolean expressions, as in is a Python keyword returning True or False depending on whether left operand is contained in the collection denoted by the right operand. From the documentation:

The operators in and not in test for collection membership. x in s evaluates to true if x is a member of the collection s, and false otherwise. x not in s returns the negation of x in s. The collection membership test has traditionally been bound to sequences; an object is a member of a collection if the collection is a sequence and contains an element equal to that object. However, it make sense for many other object types to support membership tests without being a sequence. In particular, dictionaries (for keys) and sets support membership testing.

Upvotes: 1

benjymous
benjymous

Reputation: 2122

if key in family means

if the container "family" contains "key"

In C-like languages it could be written something like

if( family.contains(key) )

Either family will contain key, or it won't. So it's a boolean expression

Upvotes: 0

neminem
neminem

Reputation: 2698

They are boolean conditions. Boolean conditions don't have to look like "if X < Y", that's just an example. A boolean condition is simply anything that evaluates to true or false. "key in family" evaluates to true if the value of "key" is in the list "family", and false otherwise.

Upvotes: 0

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