Python is a dynamically typed programming language. Whereas statically typed programming languages such as C# and Java might require type specifiers
inti=42;
Stringmessage="Hello world!";
Python infers the type of a variable from the type of the values assigned to it
i =42
message ="Hello world!"
Thus the variable i would be an integer (or int in Python) because the value assigned to i, 42, is an integer. And since "Hello world!" is a string (or str in Python) the variable message is also a string.
Note that like JavaScript, Python strings can be single or double quoted. This course will use double quotes a majority of the time.
With this in mind let’s think about what data we would need to describe a cryptocurrency transaction. First, we’ll need the name of the coin. This would be a string.
coin ="bitcoin"
We also need the amount of the coin being bought or sold. Since you can buy fractions of a coin, we’ll use a floating point number.
amount =0.5
There is no way to know if this transaction is for a buy or a sell. There are several ways to do this. Since there are only two possible values, buy or sell, we can use the boolean type. The buy variables will be True if the transaction is a buy, and False for a sell.
buy =True
Note that the built-in Python values True and False are capitalized.
The timestamp of the transaction should also be recorded. For simplicity, we’ll only record the date. This could be done with three integers, one each for the year, month and day.
Now this technically isn’t wrong, but there are better mechanisms. Using three separate values would make it difficult to compare dates. And we will also want to render them as strings like “Feb. 20, 2026”. For this, we can turn to the Python standard library. The Python language includes types for primitive values such as strings and integers. The Python standard library is a collection of modules including functionality that is often used in Python development, but not often enough to be part of the core language. It is distributed with the Python language so you can be sure of its availability. In other words, when you install Python, you get the Python standard library without any addition installations. The Python standard library includes the datetime module for working with dates and times.
import datetime
The import keyword makes the members of the datetime module available for use. An instance of the date type can be created by providing integers for the year, month and day.
timestamp = datetime.date(2026,2,20)
The date type also allows you to compare two dates with comparison operators. It has methods to render a date as a string and to parse a date from a string. We’ll see some of these next.
We now have enough data to represent a cryptocurrency transaction. Let’s see how to display it to the user.
To get started, we will use the built-in print function. print accepts a value. The string representation of that value will be displayed in the console. For the primitive data types, the output is predictable.
print(coin) # bitcoin
print(amount) # 0.5
print(buy) # True
Note: A single line comment in Python is preceded with the # character
The date object is a little different.
print(timestamp) # 2026-02-20
The default string representation of a date is the four digit year, a hypen, the zero padded numeric month, another hypen, and the zero padded numeric day. By calling the strftime method on the date and passing it a format string, you can have precise control over the string representation. For example, this format string "%b. %e, %Y" will display the abbreviated month, a period, a space, the numeric day without padding, a comma, a space, and the four digit year.
Displaying the values by themselves is not enough. You need to add context by embedding the variable values in a string. In Python, you can do this by formatting the string with something known as an ‘f-string’. Here is an example.
print(f"Transaction for {amount}{coin} on {timestamp.strftime('%b. %e, %Y')}")
# Transaction for 0.5 bitcoin on Feb. 20, 2026
First, it’s obviously how the f-string gets its name. The formatted string is prefixed with the letter ‘f’. Inside the f-string, Python expressions in curly braces are evaluated and then result inserted into the string. For variables this is the string representation. But you can also call the strftime method as well. Notice that the format string passed to strftime is single quoted otherwise Python would get confused. You could also have left the format string passed to strfine double quoted and single quoted the f-string.
There one more data point we didn’t show in the f-string, the buy variable. As a boolean the string representation will be either True or False. And we can do this.
print(f"{buy}{amount} of {coin} on {timestamp.strftime('%b. %e, %Y')}")
# True 0.5 of bitcoin on Feb. 20, 2026
Without context this doesn’t make much sense. Instead, we’d like the output to be “Bought” or “Sold” depending on the value of buy. We’ll need a conditional for this.
if buy ==True:
action ="Bought"
else:
action ="Sold"
The syntax here is the if keyword, followed by the condition without parentheses. Then a colon to indicate the next line starts the body if the conditional evaluates to True. The body must be indented. Indentation determines scope.
Note: As Python uses indentation to determine scope, it is very picky and expects consistency. Both the size and character used in the indentation should remain constant throughout the code. For example, don’t use 2 spaces sometimes and tabs of width 4 in others, even if it looks better. Python will raise exceptions for inconsistent indentation.
Putting this together with the f-string will add context to the buy variable.
if buy ==True:
action ="Bought"
else:
action ="Sold"
print(f"{action}{amount} of {coin} on {timestamp.strftime('%b. %e, %Y')}")
# Bought 0.5 of bitcoin on Feb. 20, 2026
It turns out, you can evaluate the action in a single line expression with a ternary conditional.
"Bought"if buy ==Trueelse"Sold"
The ternary conditional can be directly evaluated in the f-string
print(f"{'Bought'if buy ==Trueelse'Sold'}{amount} of {coin} on {timestamp.strftime('%b. %e, %Y')}")
The standard adminition of “With great power comes great responsibility” applies here. Take care not to get too clever and make your code unreadable.