Practical-Python fundamentals - using conditional statements and loop structures

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Transcript

Hi, I'm going to show you how to work with conditional statements and loop structures in Python. However, let's make a review of the fourth lesson. In the previous lesson, I showed you that Python works with two data type structures, lists and tuples. Remember, the values and length of list can be modified After you create them, but tuples are immutable, so you cannot change them after that. As I said before, In this tutorial, we work with controlled work flow structures. However, we need to learn about boolean data type and it's operators.

A boolean data is a data type that handles only two values in Python are noted true and false. So they represent the outcomes of logic and Boolean algebra. Python has three Boolean operators and or not. It also has several comparison operators. The most commonly used are equal to not equal to, greater than, less than, greater than or equal to, less than or equal to. Keep in mind, when you compare two values, you will get a boolean data true or false.

These operators are used to make conditional statement. For example, If you set the variable x to number four, and compare this value to 10, you can make some comparison statement is x greater than 10, right, x greater than and the number 10. Then press enter. You would get false since x is less than 10. Here is another example, is 40 divided by 20 multiplied by four less than or equal to minus four, elevated to the power of two, the outcome is false. We compared eight to minus 16.

Next, make other comparisons And see the outcomes? How can you control the workflow in Python using conditional statement? Well suppose that you need to make a decision to take one way or another. To make this possible, you have to make a condition statement using the word at the beginning and a colon at the end of the instruction. So when you make a conditional statement, you create two possible paths in the workflow. One, if the statement is true, and another or false.

In this sense, you run a code block if the expression is true, while if the outcome is false. You can run another block or do nothing. Let's do some examples. First write the variable called side to the string left. Now right side, double equal sign, left, finish with a colon. When you press enter, you will notice that Python uses out of indentation, since it uses indentation.

To group these statements, the right print, open parenthesis and type the cars turn to left and close the quotes side. Then close parenthesis and press enter. You get another indentation since Python assumes Your next statement will belong to the group of the true branch. Since we won't write any other statement, press ENTER again. When you do that, you will get the message printed. Now I change the value upside to write and write the previous if statement.

For this example, Python will not print any messages in the shell, since the whole expression is false. So how can you enable the false branch in case you require to execute some action on the false condition? You have to use the else word. For example, set the variable called speed equal to 75 Press Enter, then write if speed is greater than 70. Type in a colon at the end, and press Enter. Now print a message from the true condition.

The first one is you are over the speed limit. The second one is reduce speed now. Once you write the second print statement, press enter and then press backspace to delete the indentation. After that write else, followed by a colon and press enter. Then write the message. Have a nice day and press two times.

Enter Python We'll print the message of the true branch. However, if you change the value of speed to 60 and run the if statement again, the outcome will be Have a nice day. If you need to nest if statement, you can use the else if use this structure to false condition nested by another if statement. Keep in mind, else instruction is for both expressions. So set a variable called X to five, right if x is less than or equal to four and press enter, print the value is less than one or equal to four and press enter. After that, press backspace, write else if x less than six, and press enter.

Print the value is greater than four, but less than six and press enter. Then press backspace again, right else, followed by a colon and press enter. print the value is greater than six, and press Enter twice. Now suppose that you need to repeat the last code loop for different values of x. It will be very impractical if you copy and paste this block of code several times for each value So you have to work on loop statement. In those cases.

Python works with two types of loops for and while in this sense, use the four structures when you need to run an action or group of them many times. In other words, the for loops, repeats a block of code for each element from the list. So you need to create one when you use it. In case you work with numerical list, you use the range function. Let's do an example. Using for loop create a list called format, which has the strings be MPJP G, P and G and T i, f f, then write for extension in formats colon and press enter.

Python will use automatic indentation to prove the block of code inside the loop. Now print the image file format combined by extension. Press Enter twice and observe the outcomes on the shell. Notice that Python printed four messages, since the list has four file formats. To keep in mind that each value of the list is assigned to the variable called extension. Here's another example.

Right for x In range, open parenthesis, zero, comma 10, close parenthesis, type colon and press Enter. Now print the square value of closed quotes, and then call the structure function to x combined with the string is, after that, write the function pow, open parenthesis, write x, comma to close parenthesis and apply stroke function to that. Finally, combine it with the previous strings and press Enter twice. Check the outcomes. If you use a third argument. This will represent the state Between each value of the list.

On the other hand, use the while statement when you need to control the loop since the number of repetition is unknown, while the condition is true, Python repeats the code block, but it breaks the loop when the condition is false. Keep in mind that Python verifies the condition before entering the loop. Also, you'll get an infinite loop if you never reach the condition. Let's do examples using while loop. First, set the variable i to zero right while i less than or equal to 10 colon and press Enter Then print I and press Enter. Now right i plus equal to one and press Enter twice.

Observe the outcome. Notice the loop breaks when the variable I reached the value of 11. Print I again to check that the statement i plus equal one. Now write the same example, but set the variable i 211 and observe the outcome. In this case, the code block will never run, since the value of AI generates a fault condition and breaks the loop before entering what would happen if the variable AI does not have the Value increase. It never reaches 11.

Well, in that case, you get inside an infinite loop. So when this happens, press Ctrl key and C key at the same time in the shell of Python. This will break the loop. That's all for this tutorial. I hope you liked it. And you want to learn more tutorials about Python and GIS

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