Tag: Python

You can follow along with the code from Github.

• A tuple consists of a number of values separated by commas.

Tuple Packing and Unpacking

• In Python we can pack the tuple by putting values into a new tuple
• Unpacking a tuple is when we extract its values into a single variable.

List Vs Tuples

• Lists are mutable – They can be changed or modified after creation according to the developers needs.
• Tuples are immutable – they can’t be changed or modified after creation.
• List have more operations (functions) available to them.
• Syntax is different

• A special problem is the construction of tuples containing 0 or 1 items: the syntax has some extra quirks to accommodate these. Empty tuples are constructed by an empty pair of parentheses; a tuple with one item is constructed by following a value with a comma (it is not sufficient to enclose a single value in parentheses).

You can follow along with the code from the Github.

• Del – The del statement in python is used to delete objects. In Python everything is an object, so the del keyword can also be used to delete variables, lists, or parts of a list etc.
• Notice the output as you follow along the code flow.

• Data structures are used to store a collection of related data. There are four built-in data structures in Python – list, tuple, dictionary and set.
• ***NOTE: It is sometimes tempting to change a list while you are looping over it; however, it is often simpler and safer to create a new list instead.***

Lists as Stacks

• The last element added is the first element retrieved (“last-in, first-out”). To add an item to the top of the stack, use append(). To retrieve an item from the top of the stack, use pop() without an explicit index.

Lists as Queues

• The first element added is the first element retrieved (“first-in, first-out”); however, lists are not efficient for this purpose. While appends and pops from the end of list are fast, doing inserts or pops from the beginning of a list is slow (because all of the other elements have to be shifted by one).
• To implement a queue, use collections.deque which was designed to have fast appends and pops from both ends.
• Notice the queues only can pop from left to right.

List Comprehensions

• <+Make new lists where each element is the result of some operations applied to each member of another sequence or iterable, or to create a subsequence of those elements that satisfy a certain condition.

• Note that this creates (or overwrites) a variable named x that still exists after the loop completes. We can calculate the list of squares without any side effects.

• A list comprehension consists of brackets containing an expression followed by a for clause, then zero or more for or if clauses. The result will be a new list resulting from evaluating the expression in the context of the for and if clauses which follow it. For example, this listcomp combines the elements of two lists if they are not equal.
• Notice that the order of the for and in statements are in the same order in both of the examples.

Methods for List Objects

• append – Used to add an object to the end of a list.
  ***Notice append will only take one argument at a time.***

• extend – Extends a list by adding all items from the iterable.
  ***Notice the difference between append and extend.***

• insert – Inserts the object into a list at a given index. (0 = beginning of the list)

• remove – Removes an object from a list. You must specify the object to be removed. If it is a string you must specify the sting.

Clear – Clears all objects out of a list.

• index – locate and search for an object within the list starting at a given index.

https://github.com/rfc-1925/Python

• An argument (also known as an arg) is data that can be push into a function.
• The function must be called with the exact number of arguments that it is expecting. Notice the error received.
• The code also uses the ‘in’ keyword. This keyword tests whether or not a sequence contains a specific value. The values are evaluated at the function definition within the defining scope.
• Python allows functions to be called using keyword arguments. When we call functions in this way, the order (position) of the arguments can be changed. One can think of the keyword arguments (kwargs) as being a dictionary that maps each keyword to the value that we pass alongside it. That is why when we iterate over the kwargs there doesn’t seem to be any order in which they were printed out.
• The form is kwarg=value

• Now notice when we call the function with the proper number of arguments we no longer receive the error.
• ***The reason we are not having to pass the ‘reminder’ argument is explained next.***

Default Arguments

• Default arguments are used so that a function can be called with fewer arguments than it is defined to allow.
• In the past example we needed to pass the argument ‘retries’ or else we would receive an error.

• Now if we change our default value the number of times the function iterates is different. Why?

• Notice that the default value is evaluated only once.

• when the default is a mutable object such as a list, dictionary, or instances of most classes the function accumulates the arguments passed to it on subsequent calls.

• Python is a high-level, interpreted, interactive and object-oriented scripting language. Python is designed to be highly readable. It uses English keywords frequently where as other languages use punctuation, and it has fewer syntactical constructions than other languages.

• It supports functional and structured programming methods as well as OOP.
• It can be used as a scripting language or can be compiled to byte-code for building large applications.
• It provides very high-level dynamic data types and supports dynamic type checking.
• It supports automatic garbage collection.
• It can be easily integrated with C, C++, COM, ActiveX, CORBA, and Java.

Interpreter

• The interactive interpreter can be used by executing the version of python you are running. Executing python3 will drop you into whatever version of python 3 you have installed.

• Python can do basic to complex mathematics functions built into the interpreter.

• You MUST define a variable in order to call it.

More Fun With The Interpreter

• Take a moment to see the output from each input.

Hello World

• You don’t have to use the interpreter but do be aware of it.
• In the below screenshot we are using Visual Studio Code and running the script in interpreter after.