Lesson 3 reading

You have been using print since day one, but it has more to say. This reading is a tour of its options — all of them about the same question: how do I get the output to look exactly the way I want?

Printing several things at once

So far we mostly printed one thing per call. But print happily takes several values separated by commas — and they can mix text literals and variables freely:

age = 12
print("I am", age, "years old")

I am 12 years old

Notice two gifts you got for free. First, print put a space between each value — you didn't type those spaces. Second, it printed a string and an int side by side without complaint.

That second gift is bigger than it looks. Try gluing them with + instead:

age = 12
print("I am " + age)

Traceback (most recent call last):
  File "print_age.py", line 2, in <module>
    print("I am " + age)
          ~~~~~~~~^~~~~
TypeError: can only concatenate str (not "int") to str

The same type rule from Lesson 2: + refuses to mix str and int, exactly like "2" + 2. You would have to write "I am " + str(age). The comma skips all that — print converts everything to text for you.

You have already seen the comma in action, by the way — the even/odd printer in the Lesson 2 reading used print(i, "even").

sep — choosing the separator

That automatic space between values is just a default, and defaults can be changed. The separator argument is called sep:

print("2026", "07", "27", sep="-")

2026-07-27

Or squeeze the values together with nothing at all:

print("ha", "ha", "ha", sep="")

hahaha

end — choosing the ending

You know this one from the lesson: print normally ends by pressing Enter, and end="" cancels that so the next print continues on the same line.

sep and end are answering two different questions: sep is what goes between the values inside one print, and end is what goes after the whole thing. One call can use both:

print("2026", "07", "27", sep="-", end="!")

2026-07-27!

f-strings — the precise way

The comma is easy but it controls nothing — you get a space between values whether you want one or not. When you want a sentence to come out exactly right, Python has a nicer tool: put the letter f in front of the string, and inside it, anything wrapped in curly braces {} is treated as Python instead of text:

age = 12
print(f"I am {age} years old")

I am 12 years old

Python replaces {age} with the value of age. No commas, no str() conversion, no surprise spaces — the string looks like the sentence you want, with blanks filled in.

And the braces hold any expression, not just a variable name — math works in there:

age = 12
print(f"Next year I will be {age + 1}")

Next year I will be 13

The f matters. Forget it and Python prints the braces literally — I am {age} years old. If your output ever shows curly braces you didn't want, that missing f is the first thing to check.

Which one should you use? For quick checks and debugging — like printing a loop's variables to watch them change — commas are fastest to type. For output a person is meant to read, f-strings say exactly what you mean.

Try it

Before running each one, predict the exact output — spaces, dashes and all. Then run it and check yourself:

name = "Scott"
age = 12
print(name, "is", age)

print("A", "B", "C", sep="...")

for i in range(3):
    print("ha", end="")
print()
print("done")

item = "pencil"
price = 2
print(f"One {item} costs ${price}, two cost ${price * 2}")