Creating Our First Python Program
Tags: python, tutorial, beginners, codenewbie
Published: 2020-02-03 02:24:06

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Python is a convenient language that’s often used for scripting, data science, and web development.

In this article, we’ll look at how to create our first Python program.

Our First Program
=================

We can create a program that asks us our name and then displays a greeting with our name as follows:

```python
print('What\'s your name?')
name=input()
print('Hello', name)
```

In the code above, we called the `print` function to show the `What's your name?` message. we have a `\` before the `'` to indicate that we aren’t closing the quotes with the single quote.

Then we call the `input` function to get the value that’s inputted with the keyboard.

Once we press Enter, then the `name` variable will be assigned to what we’ve entered.

Then we display `Hello` and then whatever we entered before.

For example, if we entered `Joe` then we get `Hello Joe` displayed on the screen.

If we want to add an input for age and display it, we can rewrite the program to be the following:

```python
print('What\'s your name?')  
name=input()  
print('What\'s your age?')  
age=input()  
print('Hello', name, 'You are', str(int(float(age))), 'years old')  
print('The length of your name is', str(len(name)))
```

In the code above, we added an `age` input with:

```python
age=input()
```

Then we converted the inputted`age` to a float with `float` , then we converted it to an integer with `int` , then we convert it back to string with the `str` function.

We did that to round any decimals to a whole number.

Then we use `print` to display everything in English.

Then we get something like:

```
What's your name?  
Joe  
What's your age?  
20.2  
Hello Joe You are 20 years old
```

Where `Joe` and `20.2` are what we entered.

Parts of our Program
====================

A program consists of multiple parts.

Comments are one part of a program that serves as documentation that explains what we want to do with the program.

Python ignores comments, which starts with `#` .

It’s also used to temporarily remove a line before running a program for debugging purposes.

Python also ignores blank lines after the comment, we can add more blank lines to make our program easier to read.

The print() Function
--------------------

The `print` function lets us print strings on the screen. We can separate the parts of our string with parentheses.

We did that above with:

```python
print('What\'s your name?')
```

and:

```python
print('What\'s your age?')
```

and:

```python
print('Hello', name, 'You are', str(int(float(age))), 'years old')
```

Note that everything we passed into the `print` function must be strings. The end quotes are delimiters for our string.

We can print a blank line by passing nothing to the `print` function.

The input() Function
--------------------

The `input` function lets us take in input from users by letting the typing it in on the screen.

It returns a string with the things that are typed.

We get the name with `name=input()`, and then passed it into the `print` function to print it out.

The len() Function
------------------

The `len` function lets us get the length of a string by passing in a string.

In the example above, we have:

```python
print('The length of your name is', str(len(name)))
```

to get the length of the `name` string and print it out.

So for `'Joe'`, it’ll be 3.

The str(), int(), and float() Functions
---------------------------------------

The `str` function was used to convert any non-string expression to a string.

Likewise, `int` and `float` are used to convert something an integer and floating-point number respectively.

For example, we can convert a float to an integer by writing:

```python
int(1.11)
```

then we get 1.

If we try to convert something that can’t be converted to an integer as follows:

```python
int('11.99')
```

We’ll get the following error:

```
ValueError: invalid literal for int() with base 10: '99.99'
```

Likewise, we can convert something to a floating-point number as follows:

```python
float('11.99')
```

Then we get `11.99` returned.

We can pass in any other expressions into functions not just literals like strings and numbers.

Conclusion
==========

We can print strings out to the screen with the `print` function. It takes any number of strings separated by parentheses.

To get input from a user, we can use the `input` function, which returns a string with whatever is entered by the user after they press enter.

To get the length of a string, we can use the `len` function, which takes a string that we want to get the length for as an argument.

To convert something to a string, we use the `str` function. Likewise, we convert to a floating-point number with the `float` function, and an integer with the `int` function.

In addition to code, we can put comments in our Python program, which are ignored by the Python interpreter. They start with a `#` sign.