For negative indexing, to display the 1st element to last element in steps of 1 in reverse order, we use the [::-1]. The [::-1] reverses the order.
[-1] means the last element in a sequence, which in this is case is the list of tuples like (element, count) , order by count descending so the last element is the least common element in the original collection. – khachik.
Summary. The double colons ( :: ) in Python are used to specify how a slice operation should work. They can be used to slice through some data collections.
For any iterable in python [-4:] denotes the indexing of last four items of that iterable.
string[::2] reads “default start index, default stop index, step size is two—take every second element”.
With this knowledge, [::3] just means that you have not specified any start or end indices for your slice. Since you have specified a step, 3 , this will take every third entry of something starting at the first index. For example: >>> '123123123'[::3] '111'
Colons are an important part of Python syntax, used to indicate the beginning of a code block in conditional statements (if, elif, else), loops (for and while), dictionary data structures, function definitions and class definitions.
It means, "start at the end; count down to the beginning, stepping backwards one step at a time."
Python 2 stores strings by ASCII; Python 3 uses Unicode. Python 2 has a more complex syntax than Python 3. Many Python 2 libraries aren't forward compatible; many libraries exclusively use Python 3. Python discontinued Python 2 support in January 2020; Python 3 remains the most popular choice.
Double Trailing Underscore __var__ : Indicates special methods defined by Python language. Underscore _ : Used as a name for temporary variables.
Introduction. A list is a data structure in Python that is a mutable, or changeable, ordered sequence of elements. Each element or value that is inside of a list is called an item. Just as strings are defined as characters between quotes, lists are defined by having values between square brackets [ ] .
In Python, the List “-1” index shows the usage of negative indexing, which means the last value of the specified list. The Python List “-1” index is a useful tool for accessing and removing the last value in a list. The “-1” index can cause errors if we apply it to an empty list.
In general, it takes around two to six months to learn the fundamentals of Python. But you can learn enough to write your first short program in a matter of minutes. Developing mastery of Python's vast array of libraries can take months or years.
When reading, list is a reference to the original list, and list[:] shallow-copies the list. When assigning, list (re)binds the name and list[:] slice-assigns, replacing what was previously in the list. Also, don't use list as a name since it shadows the built-in. Save this answer.
arr[-1] will be 68 , arr[-2] will be 15 , arr[-3] will be 66 , and so on. When you write arr[n] (where n is a number), python will take the nth element of arr (python counting doesnt start with 1, but with 0).
The __init__ method is the Python equivalent of the C++ constructor in an object-oriented approach. The __init__ function is called every time an object is created from a class. The __init__ method lets the class initialize the object's attributes and serves no other purpose. It is only used within classes.
Python 4.0 will probably never come — according to the creator of Python, Guido van Rossum. The lessons learned from migrating from Python 2 to Python 3 demonstrated what a hassle it is to move to a new language version. Thus, there will probably not be a new version of Python soon.
Why should you learn Python 2? While you may not find much Python 2 code in use, you may still run into it from time to time. Most companies have what they call legacy code. This is code that is already working, and development on it has finished except for fixing bugs that may pop up once in a while.
So is Python 3 faster than Python 2? Yes! in almost all tests. The notable exceptions were the crypto_paes test, where Python 3 was 1.35x slower (because of the integer types), python_startup as 1.39x slower.
It is a mathematical notation for an "open range" or "half closed interval". The notation has no use in common programming languages, including Python. In this case, it means "all the representable numbers between 0 and 1, excluding 1". Follow this answer to receive notifications.
As for why 1.0 == 1 , it's because 1.0 and 1 represent the same number. Python doesn't require that two objects have the same type for them to be considered equal.
+= Operator Python: Numerical Example
The alternative is using a plus sign to add two values and the equals sign to assign the value to a variable. First, we declare a Python variable called a. This variable stores the value 10. Then, we use a += 7.5 to add 7.5 to the a variable.
In Python, a colon is required at the beginning of every block of code. It is easier to explain with an example. If I want to run code only if a certain condition is true then I want to use an if statement. An if statement looks like if condition: code code code. Notice how at the end of the if statement I have a colon ...
Python does not require semi-colons to terminate statements. Semicolons can be used to delimit statements if you wish to put multiple statements on the same line. A semicolon in Python denotes separation, rather than termination. It allows you to write multiple statements on the same line.
Python is supposed to be clean and readable. Syntactic characters like semi-colons add unnecessary clutter. If you send a code like this to an experienced Python programmer, you will never hear the end of it. Forcing multiple statements onto one line makes a trivial code harder to read.