Pyladies Workshop 2: Variables and simple data types

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Welcome to the second workshop of Pyladies - Ho Chi Minh chapter!

This time we will continue to learn more about Python by starting with simple examples and working in pairs to help each other understand instruction and complete excercise.

Most of content in this workshop is adapted from "Python Crash Course: A Hands-on, Project-based Introduction to Programming" by Eric Matthes and "Developer Class" by Google in python 3.

Feel free to reach out to us if you have any question. And don't forget to ask two people sitting next to you for some (unexpected but super helpful advice)!

Outline

0. Zen of Python
1. Examples of variables
2. How to name and use variable
3. Understand String
4. Understand Number
5. Combine String and numbers
6. Review

Zen of Python

Pythonistas, a Pythonic way to called Python users, love simplicity and readability. Our philosophy is that the code should be beautiful and elegant. Try to run the following code to get a The Zen of Python by Tim Peters

import this

One of the most important take-away notices for you is that

Now is better than never

Again, we would emphasize that the best way to learn and practice Python is starting with a simple and workable code for any project rather waiting until learning every details but never know when it would end. That's why Pyladies is here to help :)

What are variables and some examples

Let us illustrate how to use a variable in by a very simple program.

message = "Hello Python world!"
# Notice: in PEP8, double quotes are used for human reading
print(message)

Run the above in your Jupyter Lab and let us know what happens. To explain, we have already created a variable named message. In general, each variable is associated to a value. In this example, "Hello Python world!" is a string attached to message. And if you change a value of variable, it will be updated the newest.

How to name and use variables

Some rules to help you

• Names of variable can contain letters, numbers and underscores. However, numbers and score can not used at the beginning of variable. For example, message_1, but NOT 1_message

• We don't use space, instead underscore. For example, message_1, but NOT message 1

• Avoid using Python keywords or function names, unless a new value will linked. For example, do not use list to name a list of things. Use an descriptive names, such as list_of_words

• Following the above idea, please use names which is informative, not representative such as message_id rather than id

• Note: In PEP8, we use lower case for name of variables such as message_id, new_message. It will be fine if you use upper case, however, the reason why we make this regularization is for a sake of common style.

Understand string

String is simply defined as a series of characters enclosed by a pair special characters. Indeed, there are three of them, e.g. ", ", and """ with respect to double quotes, astrophes and triple quote. So, what is a difference

"Hello! I am a pythonista."
'Hello! I am a pythonista.'

Manipulated with string

string or str as a built-in class is supported in Python with a lot of features. For example,

• len: returns a length of a string
• str: convert a non-string object to string object
• Indexing: Assume that you have a string called message. You can take an element or a list of elements inside that string out by message[i]
• Concatenation: Combine two string as one by +

Another nice things of string are built-in methods allowing you to "fly in the sky" You might want to see the most common which I stole from Google Developer Class in the following classes:

• s.lower(), s.upper() -- returns the lowercase or uppercase version of the string
• s.strip() -- returns a string with whitespace removed from the start and end
• s.isalpha()/s.isdigit()/s.isspace()... -- tests if all the string chars are in the various character classes
• s.startswith('other'), s.endswith('other') -- tests if the string starts or ends with the given other string
• s.find('other') -- searches for the given other string (not a regular expression) within s, and returns the first index where it begins or -1 if not found
• s.replace('old', 'new') -- returns a string where all occurrences of 'old' have been replaced by 'new'
• s.split('delim') -- returns a list of substrings separated by the given delimiter. The delimiter is not a regular expression, it's just text. 'aaa,bbb,ccc'.split(',') -> ['aaa', 'bbb', 'ccc']. As a convenient special case s.split() (with no arguments) splits on all whitespace chars.
• s.join(list) -- opposite of split(), joins the elements in the given list together using the string as the delimiter. e.g. '---'.join(['aaa', 'bbb', 'ccc']) -> aaa---bbb---ccc

Understand numbers

Integers and floats are the most basic data types in python allowing you to work on multiplication (+), subtract (-), multiply (*) and division (/). For integers, you can make operations with exponential (**) and modular (%) and residue (//). Let us do some fun calculations

"""
Example to understand numbers with multiplication and sum
"""

def calculate_time(num_years):
    """
    A function to calculate an amount of time measured in years

    Args:
        num_years (int): number of years

    Returns:
       (int) an amount of time measured in terms of seconds by years

    """
    num_second_per_minute = 60
    num_minutes_per_hour = 60
    num_hour_per_day = 24
    num_day_per_month = 30  # Let us simplify this part by an average
    num_month_per_year = 12
    return (num_second_per_minute \
          * num_minutes_per_hour \
          * num_hour_per_day \
          * num_day_per_month \
          * num_month_per_year) * num_years

print(sum_calculation(2000))
print(sum_calculation(2000.0))

Combine String and numbers

See this example, and tell us why it is wrong

year = 2018
message = "Happy year of " + year
print(message)

How to fix this

year = 2018
message = "Happy year of " + str(year)
print(message)

Review

In the previous, you have gone through some of important aspects of Python with variable and two simple data type such as string and number. Let us do a small quiz to test our knowledge before moving to a pair-programming assignment