In Python, you can put parameters with format "key=value". In this case, you could see there is no space between "=".
At the same time if it is assigning a value to a variable you coud see the space between "=" like "variable = 1".
The reason why different using space between "=", is to increase the grepability.
For example if you want to find the line which is calling a method with key=value parameter, you're going to use below command
$grep -nr "key=" .
Otherwise, if you need to find a valiable, you will use below command.
$grep -nr "key =" .