Python Tutorial 5

 Data Types: Strings

A string is a sequence of characters. (A string can be a text, a sentence or multiple sentences, It could be a word or a single character)

Let's create a new string and learn something cool.

• Let's create a new variable called myString 

We can see the data type of our variable using the type() function.

 

• As you can see 'str' stands for string which means text!
• How did Python know we passed a string?
• ans: It's inside a quotation marks " " 

Note; Strings should always be inside quotation marks! And if you pass a number inside  quotation marks it would be stored as a string not an integer!

• lets try 40 in quotation marks and checck the data type.

• Actually this is the correct way of storing numbers that are not used for calculation. eg. kkamenyoh111@gmail.com, an invoice number or a zip code!
• We can also use a single quotation mark ' ' , you just can't mix them. When you start with a single quotation mark,  you should end with a single quotation mark and not double as this will result in problems.
• These can be useful when we want to use quotation marks inside our string.

Example:

You can see that " meet me at 5 " turned to color black instead of green.

Python thinks the string ends at " She said ", it does understand what your trying to do afterwards.

So if you want to do something like that you can use single quotation marks outside  the text, so you can use double inside.

I'm glag you're following. If you don't understand anything just leave it in the comment section and I will respond.

Okay let's continue.....

In a string every character has it's own index, starting from zero.

We can access an index by using braces [ ]. 

Steps

1. Use the name of the variable

2. Using braces we can tell the index we want to get

3. Let's get the first, second and last character

• A string also has a length(the number of characters).
• We can get the length of a string by using the len( ) function.

• Meaning we have 25 characters in our string.

More example:

With these 3 characters we know that our first character is index 0, second is 1, and third is 2.

So no matter the length of our string the last character is going to be our [ length - 1 ]

And it is going to work no matter the size of our string.

This formula is going to be very important when we start treating loops in this course!

Slicing

• We can also get part of a string using a technique called slicing.

Example:

Let's say we have a string that represents a bank account number, where the first two characters indicate the country.

As you can see first index [0 : 2] which is G is included but the second index [0 : 2] which is 2, is not not included. So we got from G to 2 but not including 2!

Example 2:

Lets put the country code in the end.

And that's how we do it.

You can try and have some more fun as much as you want.

We already talked about concatenation using the + sign.

ex. 

• We concatenated with space as seen above.
• But we have to be careful when we have different data type.

ex. 👉👉👉👉➡

• You can use either the str() function to convert the number to a string before concatenating or simply use the string quotation marks.

Now we know the basics of strings. We will learn more about strings as we advance in the course. 

SUMMARY

Python 3.7.0 (v3.7.0:1bf9cc5093, Jun 27 2018, 04:06:47) [MSC v.1914 32 bit (Intel)] on win32
Type "copyright", "credits" or "license()" for more information.
>>> myString = " Some text "
>>> #checking data type using the type function
>>> type(myString)

Output:
<class 'str'>

>>> myString = "40"
>>> type(myString)

Output:
<class 'str'>
>>> myString = ' She said " meet me at 5 " '
>>> myString

Output:
' She said " meet me at 5 " '
>>> myString[0]

Output:
' '
>>> myString[1]

'S'
>>> # let's get the last character, the last character of a string is -1
>>> myString[-1]

Output:
' '

See you in our next tutorial. Good luck!

Exercise On Variables and Input Functions

Question:

Create a program that asks the user for a number of kilometers, converts it to miles, and prints the results to the user.

To perform this exercise, you need the conversion rate:

1 mile = 1.609344 km

Good luck, and when you finish, come back here to see the solution.

 

• We are starting a new file. In your Python interpreter, go to File from the menu.
• Then select the new file where we are going to write our computer program.
• Save your file as Ex01_km2miles for easy identification.

We will get the number of km, divide by the conversion rate, and print the output.

 

Follow the red comments in the program carefully.

Now run your program:

• As you can see, our program has been beautifully executed. The user input has made our program interactive for the user.
• But you notice our program has so many decimal places, so we are going to round it using the round() function.
• So let's go back to our program and edit our program.

 When rounding the number of miles, we punctuate it with a comma (,)) and type the number of places we want to run it to.

And now we have only 4 decimal places. Fantastic, our program is working!

We will learn more functions like this when we learn about numbers.

 Summary

km = float( input("Type the number of kilometers: ") )
miles = km / 1.609344

print(km, "km = ", round(miles,4), "miles")

Output:

Type the number of kilometers: 34
34.0 km =  21.1266 miles

If you have any questions feel free to leave it in the comment section.

Good luck happy coding!

Beginner Python Tutorial 4

In this lesson, we will learn about input functions.

We are going to make our program more dynamic by getting user input! In order to do that, we are going to use the input function!

Let's create some variables:

number 1 and number 2, instead of assigning a static value to our variable, we can make it dynamic with the input function. see below!

With the input function outside the value, we will pass the instructions for the user inside parenthesis with double quotation marks, making it a string (text), i.e., "Please enter the first number: ".

Note that this time we are working with the Python interpreter!

1. Press enter! and it will ask you to type the first number. I chose 4, but you can choose any number of your choice.

2. Type or print the variable number to see the results. We can see that the value 4 has been assigned or stored in the variable number.

Let's do the same for number 2, and then we can perform some basic operations!

You can see that as we added 4 + 8, it gave us 48, and here's why: As I told you earlier, our values are stored as strings (text), so we are dealing with a data type called string. In our next lesson, we will learn more about data types in detail. 

Here's how to check the data type of a variable: just use the type function, for instance: 

Now we can see that the type of this variable is'str', which means string. 

Operators like addition (+)  work differently depending on the data type. If we have numbers, the + sign makes a sum of those numbers, but if we have strings, the + sign makes a concatenation of those strings. That's why we just put 4 and 8 together!

Here's something cool we can do with concatenation.

Let's create a variable called first name and last name, assigning a string to each variable.

Now let's use concatenation to create an email address.

I did concatenate my first name and last name with a period (. ), and I concatenated my last name with another string ("@gmail.com").

Type enter to see results!

Remember, with our numbers, we couldn't perform the right operation, and here's how to do it.

We are going to convert our user input from a string to a number.

There are two types of numbers in Python.

1. floats: numbers with decimals. eg. 53.422223

2. integers: numbers without decimals, e.g., 34

For our program, let's allow the user to type decimal numbers in the format the format he wants:

Let's convert the input to a float using the float function. 

We converted the variable from text to numbers using the float function.

Now let's get into our program from the IDE. 

Copy and replace numbers 1 and 2 from the Python interpreter, and replace them with number one on the IDE. Remember to make the conversion by adding a float function to the value of the variable. Now let's save it and see what we get:

Now our program looks flexible and organised! We can run it now and see if our program is working.

Put in your desired numbers and see if this is the working gas shown above.

Now that our program is dynamic, if we run it again and type different values in the interpreter, here's what we get:

In our next tutorial, we are going to have an exercise. Follow for more! If you have any questions, feel free to leave them in the comment section. Good luck!