Fix errors in Control Flow (#344)

* Fixes

- Warmup exercise rewording/reorganization
- Quiz text

* Fix bugs with Exercise 4

- Correct validation steps
- Handle negative numbers if target is decimal
- Reverse the final result string, since we built from right to left

* fix docstring

---------

Co-authored-by: Despina Adamopoulou <despoina.adamopoulou@empa.ch>

Author: edoardob90

02_control_flow.ipynb

@@ -26,10 +26,10 @@
     "    - [The `enumerate` built-in](#The-enumerate-built-in)\n",
     "    - [The `range` built-in](#The-range-built-in)\n",
     "- [Warm-up Exercises](#Warm-up-Exercises)\n",
-    "    1. [Write a Python program that returns the characters in a string and their indexes](#1.-Write-a-Python-program-that-returns-the-characters-in-a-string-and-their-indexes)\n",
-    "    2. [Write a Python program that returns all the numbers in a given range, __including__ the first and the last elements](#2.-Write-a-Python-program-that-returns-all-the-numbers-in-a-given-range,-including-the-first-and-the-last-elements)\n",
-    "    3. [Write a Python program that takes a list of integers and returns the square root of each of them](#3.-Write-a-Python-program-that-takes-a-list-of-integers-and-returns-the-square-root-of-each-of-them)\n",
-    "    4. [Write a Python program that takes an integer and divides it by 2 until the result is no longer an even number](#4.-Write-a-Python-program-that-takes-an-integer-and-divides-it-by-2-until-the-result-is-no-longer-an-even-number)\n",
+    "    1. [Characters in a string](#Characters-in-a-string)\n",
+    "    2. [Range of integers](#Range-of-integers)\n",
+    "    3. [List of squares](#List-of-squares)\n",
+    "    4. [Divide by two](#Divide-by-two)\n",
     "- [Altering loops](#Altering-loops)\n",
     "  - [`if` statement inside `for`/`while`](#if-statement-inside-for/while)\n",
     "    - [Exercise: conditionals inside loops](#Exercise:-conditionals-inside-loops)\n",
@@ -91,7 +91,7 @@
    "id": "5",
    "metadata": {},
    "source": [
-    "Python [supports](./01_basic_datatypes.ipynb#Comparison-operators) different comparison expressions.\n",
+    "Python supports different [comparison expressions](./01_basic_datatypes.ipynb#Comparison-operators).\n",
     "They are called **logical expressions** as they evaluate to either `True` or `False`.\n",
     "\n",
     "We can use these results in **conditional statements**, and have our program behave differently based on the result."
@@ -586,7 +586,8 @@
    "id": "31",
    "metadata": {},
    "source": [
-    "#### 1. Write a Python program that returns the characters in a string and their indexes\n",
+    "### Characters in a string\n",
+    "Write a Python program that returns the characters in a string and their indexes.\n",
     "\n",
     "\n",
     "<div class=\"alert alert-block alert-warning\">\n",
@@ -616,8 +617,8 @@
     "\n",
     "    Returns:\n",
     "        - A list of tuples where each tuple contains:\n",
-    "            - index (int): The position of the character in the string\n",
-    "            - char (str): The character at that position\n",
+    "            - char (str): A string's character\n",
+    "            - index (int): The position of that character in the string\n",
     "    \"\"\"\n",
     "    return"
    ]
@@ -629,7 +630,9 @@
     "tags": []
    },
    "source": [
-    "#### 2. Write a Python program that returns all the numbers in a given range, including the first and the last elements\n",
+    "### Range of integers\n",
+    "Write a Python program that returns all the numbers in a given range, including the first and the last elements.\n",
+    "When we say *increasing* or *decreasing*, we mean the **canonical** (or natural) ordering of integers.\n",
     "\n",
     "<div class=\"alert alert-block alert-warning\">\n",
     "    <h4><b>Note</b></h4>\n",
@@ -670,15 +673,17 @@
     "tags": []
    },
    "source": [
-    "#### 3. Write a Python program that takes a list of integers and returns the square root of each of them\n",
+    "### List of squares\n",
+    "\n",
+    "Write a Python program that takes a list of integers and returns the square root of each of them.\n",
     "\n",
     "<div class=\"alert alert-block alert-info\">\n",
     "    <h4><b>Hints</b></h4>\n",
     "    <ul>\n",
     "        <li>You can use the <code>math.sqrt</code> function to compute the square root of a number</li>\n",
     "        <li>If a number does not have a square root in the real domain, you should skip it</li>\n",
     "    </ul>\n",
-    "</div>"
+    "</div>\n"
    ]
   },
   {
@@ -714,7 +719,9 @@
    "id": "37",
    "metadata": {},
    "source": [
-    "#### 4. Write a Python program that takes an integer and divides it by 2 until the result is no longer an even number"
+    "### Divide by two\n",
+    "\n",
+    "Write a Python program that takes an integer and divides it by 2 until the result is no longer an even number"
    ]
   },
   {
@@ -1933,7 +1940,7 @@
    "name": "python",
    "nbconvert_exporter": "python",
    "pygments_lexer": "ipython3",
-   "version": "3.10.15"
+   "version": "3.12.12"
   },
   "toc-autonumbering": false,
   "toc-showmarkdowntxt": false,

tutorial/quiz/control_flow.py

@@ -7,10 +7,10 @@ def __init__(self, title=""):
             question="""What would be the output of the following code?
                 <pre><code class="language-python">
                     if 'blue' in {'red': 1, 'blue': 2, 'green': 3}:
-                        print(1, end=", ")
-                        print(2, end=", ")
+                        print(1)
+                        print(2)
                         if 'd' in 'abc':
-                            print(3, end=", ")
+                            print(3)
                     print(4)
                 </code></pre>
             """,

tutorial/tests/test_02_control_flow.py

@@ -379,24 +379,24 @@ def reference_base_converter(number: str, from_base: int, to_base: int) -> str:
         err = "Invalid empty input"
         raise ValueError(err)
 
-    # Same to and from bases
-    if from_base == to_base:
-        return number
-
     # Handle negative numbers
     is_negative = number.strip().startswith("-")
     number = number.strip().removeprefix("-")
 
-    # Remove spaces and convert to uppercase for consistency
-    number = number.replace(" ", "").upper()
-
     # Validate digits
     valid_digits = "0123456789ABCDEF"
     for digit in number:
         if digit not in valid_digits[:from_base]:
             err = f"Invalid digit '{digit}' for base {from_base}"
             raise ValueError(err)
 
+    # Same to and from bases
+    if from_base == to_base:
+        return number
+
+    # Remove spaces and convert to uppercase for consistency
+    number = number.replace(" ", "").upper()
+
     # Convert to base 10
     decimal = 0
     for digit in number:
@@ -407,7 +407,7 @@ def reference_base_converter(number: str, from_base: int, to_base: int) -> str:
         return "0"
 
     if to_base == 10:
-        return str(decimal)
+        return f"-{str(decimal)}" if is_negative else str(decimal)
 
     # Convert to target base
     result = ""
@@ -416,6 +416,9 @@ def reference_base_converter(number: str, from_base: int, to_base: int) -> str:
         result += valid_digits[digit]
         decimal //= to_base
 
+    # We built the number from the rightmost digit to leftmost, so we need to reverse the final string
+    result = result[::-1]
+
     return f"-{result}" if is_negative else result