Python — Hello, World

A progressive introduction to printing, string manipulation, formatting, and module imports in Python.

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Learning Objectives

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Task-by-Task Reference

Each task below highlights the unique challenge it posed and the new technique introduced to solve it — techniques from earlier tasks are not repeated. Use this as a quick revision guide.

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Task 0 — Print a String (2-print.py)

Challenge: Print a string containing double-quote characters and a newline — without adding an extra trailing newline beyond what the content specifies.

Approach: Call print() with the literal string including an embedded \n escape sequence. Pass end='' to suppress print's automatic trailing newline, so the output ends exactly where the embedded newline places it.

New techniques introduced:

Key takeaway: print() adds a newline by default unless you override it with end="". Use \n to insert explicit line breaks within a string.

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Task 1 — Print an Integer (3-print_number.py)

Challenge: Embed a variable's integer value directly inside a human-readable sentence without manual string concatenation or type casting.

Approach: Use an f-string — prefix the string with f, then wrap the variable number in curly braces {number}. Python evaluates the expression inline and produces a single formatted string.

New techniques introduced:

Key takeaway: f-strings (Python 3.6+) are the cleanest way to embed variables in strings. Anything inside {} is evaluated as a Python expression.

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Task 2 — Print a Float (4-print_float.py)

Challenge: Display a floating-point number rounded to exactly 2 decimal places — controlling precision in the output without modifying the underlying variable.

Approach: Use an f-string with a format specifier: {number:.2f}. The .2f tells Python to format the float with 2 digits after the decimal point.

New techniques introduced:

Key takeaway: Format specifiers like :.2f give you fine-grained control over how numbers appear in output. f stands for fixed-point notation.

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Task 3 — Repeat and Slice a String (5-print_string.py)

Challenge: Print a string three times in a row, then print only its first 9 characters on the next line — all from a single variable assignment.

Approach: Use string repetition (str * 3, expressed via f-string as {str}{str}{str}) and string slicing (str[:9]) to extract the first 9 characters.

New techniques introduced:

Key takeaway: Python strings support slicing with [start:stop] syntax. Omitted start defaults to 0; omitted stop defaults to the string's length.

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Task 4 — Concatenate Strings (6-concat.py)

Challenge: Build a sentence by joining three separate string pieces, with spaces between the words.

Approach: Use the + operator to concatenate strings. Insert a literal space " " between variables to separate words: str1 + " " + str2.

New techniques introduced:

Key takeaway: The + operator on strings performs concatenation (not numeric addition). You must manually include spaces — Python does not insert them automatically.

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Task 5 — Extract Substrings (7-edges.py)

Challenge: Extract three different slices from a single string: the first 3 characters, the last 2 characters, and everything except the first and last character.

Approach: Use three slice variants: word[:3] (first 3), word[-2:] (last 2 using negative indexing from the end), and word[1:-1] (middle, omitting the extremes).

New techniques introduced:

Key takeaway: Negative indices count backward from the end of the string. str[-1] is always the last character regardless of string length.

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Task 6 — Advanced Slicing & Reassembly (8-concat_edges.py)

Challenge: Reconstruct a brand-new sentence by extracting three non-contiguous slices from a long string and concatenating them in a different order.

Approach: Chain three slice operations — str[39:66], str[106:112], str[:6] — and combine them with +. The result reorders the original text into a completely new phrase.

New techniques introduced:

Key takeaway: Slicing is non-destructive — the original string is never modified. You can extract, reorder, and reassemble slices to build entirely new strings.

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Task 7 — Import a Module (9-easter_egg.py)

Challenge: Display "The Zen of Python" poem without writing it yourself — leverage Python's built-in module that contains it.

Approach: Use import this — Python's famous Easter egg. The this module prints the Zen of Python automatically upon import, with no additional code needed.

New techniques introduced:

Key takeaway: Python ships with many built-in modules (this, math, sys, etc.). import gives you access to their contents without installing anything.

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Technique Inventory

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Resources

• 7. Input and Output — Python Docs
• f-strings — Python 3 Formatted String Literals
• Format Specification Mini-Language
• Common String Operations — Python Docs
• The this module — Python Easter Egg