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Sim Greenbaum
Sim Greenbaum

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Programing languages

Learning any programming language is not just about the syntax but more about what is really going on under the hood. pass by value, pass by reference, mutable or immutable. Why is this so important?

You might say why, I can write and read the code? If you don’t understand what is really going on you will be very confused by many of the bugs and will even have trouble finding them.

Mutable - the value can be changed
Immutable - the value cant be changed
Pass by value - the variable contains the value
Pass by reference - the variable just points to a place in memory that holds that piece of data.


In Ruby, strings can be mutated this means we can directly change the string, let’s say there is a spelling mistake in the string you can just access it and make a direct change

string = "hellyworld"

string[4] = "o"

stirng => "helloworld"

In python a string is immutable and can't be changed if we try to run the above code we will get an error

TypeError: 'str' object does not support item assignment

which means strings cant to be changed. We would need to slice and copy what we want and add it to a new variable

newString = string[:4] +"o" + string[5:]

newStirng >>> "helloworld"

Pass by value/ Pass by reference

In python, a variable that has an immutable (can't be changed) the value is actually saved inside the variable and if we copy one variable to another the original variable will be on touched and the addition will only affect the new variable.

For example

addString = newStirng

addString + " simcha "

This will return

>>>' helloworld simcha'

But if we check the old variable,

newStirng >>> 'helloworld'

However, a List in python which is mutable the variable is just a reference to a place in memory that holds that data so saving it to a new variable has just created a new reference to that data. Think of it like this, in Windows sometimes we create an icon on our desktop, a shortcut to a file path for quick access. If we would make a copy of the icon we are just making a copy of the shortcut, not the file. The same thing in python with mutable data variables are only a reference or a shortcut to that data. The reason for this is a list can hold thousands of pieces of data and we might be changing only one of them with index lookup

myList[35] = “change me”

Instead of loading the whole list every time we call the variable, there is just a reference that will only look at that index speeding up the execution. These concepts are not just a simple syntax but to truly understand the mechanics behind a language. If you want to be a true good developer make sure you understand these concepts well.

Stay tuned for more,

All the best,

Simcha Greenbaum

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