Python

What does [:-1] in Python actually do and why would you want to use it? [:-1] in Python is a slice operation used on strings or lists and captures all contents of the string or list except for the last character or element. Here are some examples demonstrating the operation of this code with strings: 1 2 3 >>> my_string = "Why?" >>> my_string[:-1] 'Why' As you can see from the simple code example above a variable my_string contains a string that ends with a question mark. By using the [:-1] slice operation it outputs the whole string except for the last character in the string. ...

What operator is used to raise a number to a power in Python? In Python the double asterisk operator ** is used to help calculate the exponent of a number raised to a power. This is done without a need to import the Python math library. For example, 2 to the power of 3 can be expressed using the double asterisk operator 2 ** 3, here the resulting output with the Python REPL: ...

What does the asterisk before a variable name mean in Python? For example, if I have a variable that contains a list of strings and the name of the variable is called my_list what does *my_list do? The asterisk is an operator in Python that is commonly known as the multiplication symbol when used between two numbers (2 * 3 will produce 6) but when it is inserted at the beginning of a variable, such as an iterable, like a list or dictionary, it expands the contents of that variable. ...

In Python 3.8 a new assignment expression hit allowing for easier access of variables that are used when being assigned. Here are some tips on how this can be used in your everyday coding. Wait, what’s an assignment expression? You may have heard of the term assignment operator and seen its use in the wild when doing things like incrementing a variable by 1 in Python. This is where an operator, like + or - is combined with the assignment key =. For example, x += 1 which means I’m adding the value of 1 to the variable x. ...

How do you zip two lists together in Python? What if you want to zip multiple lists together, is it the same process or something different? The built-in function zip() allows users to combine iterables, such as a list, into tuples by taking each corresponding item from the lists passed into its parameters merging the lists into one. It does not matter whether you have two or multiple lists the function are the list parameters are the same. ...

How do you initialize an empty dictionary in Python? Is it best to use dict() or {}? There are two common ways of initializing a dictionary in Python. One involves using the built-in function dict() and is known as the dict constructor, whereas the other method is known as dict literal and has the syntax {}. Here’s an example demonstrating how to initialize using both approaches in the Python REPL: ...

It can be quite easy to get the first character in a string, but how can you get the first n characters from a string? Or what about the last n characters? To get more than one character from a string you can use the slice operator which has the syntax [start:stop:step]. For example, to get the first 5 characters from a string variable my_string use the slice operator as follows my_string[:5] or to get the last 5 characters from a string use my_string[-5:]. ...

How do you increment through a for loop by 2 or more using Python? To iterate by 2 or more when processing a for loop expression use the third parameter of the range(start, stop, step) built-in function, or if using the slice operator use the third parameter. Here is an example demonstrating how to iterate through a for-loop in Python using the range() function. 1 2 3 4 5 6 7 8 9 10 11 12 13 >>> for i in range(0, 10, 1): ... print(i) ... 0 1 2 3 4 5 6 7 8 9 As you can see from the above code the range() function takes three parameters: start, stop and step. ...

How can you use the Python Regex library to check if a string represents a phone number? To check if a string matches a specific pattern use the Regex library’s match or exec methods. Before writing your Regex pattern inspect the variants for the phone number field to see whether you’re Regex pattern will match. For example, if upon your inspection you find the following variants: + 0 0 6 ( 0 1 6 4 4 1 0 2 2 1 1 1 4 2 3 3 0 2 2 1 ) 4 4 - 2 5 4 1 3 3 . 3 6 5 2 4 4 3 4 7 6 3 5 5 4 5 8 7 4 - 5 9 5 6 6 . 6 H 6 7 7 6 7 W o 7 8 8 7 8 o m 8 8 9 r e - k M u m By noting all the different variants you should be able to write your Regex pattern to capture all these types that are valid phone numbers. ...

How do you convert a string representing a percentage number into an actual number that can be used to perform calculations? To convert a string represented as a percentage number into an actual decimal number in Python use the built-in float() function after removing the percent symbol from the string and any other characters that prevent numeric conversion. Without purging from the original string the percent symbol you will get a ValueError as demonstrated below in the Python REPL: ...