#set document(title: "1.1 Mojo quickstart", author: "Modular Inc. / XYZ Homework")
#set page(width: 8.5in, height: auto, margin: 1in)
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#let BLUE = rgb("#183B6F")     // brand navy — section bars + example/solution labels (white on navy 11.09:1)
#let ORANGE = rgb("#A94509")   // brand primary-700 — AA-safe deep orange for TEXT (5.93:1 on white; raw brand #F37021 is 2.94:1 and must never carry text)
#let RED = rgb("#DC2626")      // brand error-600
#let GREEN = rgb("#059669")    // brand success-600 (decoration only; small green text uses green-text #007942)

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#let examplebox(label, title, body) = block(width: 100%, breakable: true,
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#let solutionbox(body) = block(above: 4pt, below: 8pt)[
  #text(fill: BLUE, weight: "bold", size: 8.5pt)[Solution] #linebreak() #body]

#let figph(msg) = block(width: 100%, height: 60pt, fill: rgb("#f6f7f9"),
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// degenerate 1-D shape (a bare line), and w/h or tw/w would then divide by zero.
#let _STD_W = 3.5
#let _WIDE_W = 5.6
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== 1.1#h(0.6em)Mojo quickstart


    This page quickly teaches you Mojo's syntax by focusing on code.


    For more explanation of the language features, see the Mojo get started tutorial or Mojo language basics.


    #notebox("Note", rgb("#8a94a6"), rgb("#556666"), rgb("#f7f8fa"))[
#emph[System requirements]


      You can use Mac, Linux, or Windows with WSL. For details, see the #link("https://mojolang.org/docs/requirements/")[system requirements].
]


    
=== Project setup


    You can install Mojo using any Python or Conda package manager, but we recommend either pixi or uv.


    Use the following command to install the :


    
==== uv


    + If needed, install uv:


        curl -LsSf https://astral.sh/uv/install.sh | sh
+ Create a project and install Mojo:


        uv init temperature-analyzer && cd temperature-analyzer
uv venv && source .venv/bin/activate
uv add mojo --prerelease allow
        Note that the --prerelease allow flag is required only when installing beta (or dev) builds.


    
==== pixi


    + If needed, install pixi:


        curl -fsSL https://pixi.sh/install.sh | sh
+ Create a project and install Mojo:


        pixi init temperature-analyzer \\
    -c https://conda.modular.com/max/  -c conda-forge
cd temperature-analyzer
pixi add mojo
pixi shell


    
=== Hello Mojo


    Create analyzer.mojo in your favorite IDE or editor.


    Add this to analyzer.mojo:


    
      def main():
    print("Temperature Analyzer")
    Temperature Analyzer
    Run it:


    mojo analyzer.mojo
    Insights:


    - If you see "Temperature Analyzer", your setup works.
- All Mojo executables use main() as their entry point.


    
=== Variables and data


    Update your file to add temperature data:


    
      def main():
    print("Temperature Analyzer")

    \# Square brackets tell Mojo the \`List\` type at compile time
    var temps: List\[Float64\] = \[20.5, 22.3, 19.8, 25.1\]

    print("Recorded", len(temps), "temperatures")
    Temperature Analyzer
Recorded 4 temperatures
    
=== Loops


    Print each temperature. Add to main() under the print statement:


    
      def main():
    \# ... existing code ...

    for index in range(len(temps)):  \# The range is \[0, len(temps))
        print(t"  Day {index + 1}: {temps\[index\]}°C")
    
    Insights:


    - The day is offset by 1 because the range uses zero-based indexing.
- The t"..." prefix creates a #emph[template string]: braces {} interpolate expressions directly into the output. This is useful because it avoids memory allocations for the intermediate values.


    
=== Functions


    Add this function above main() to calculate the average temperature:


    
      def calculate\_average(temps: List\[Float64\]) -\> Float64:
    var total: Float64 = 0.0
    for index in range(len(temps)):
        total += temps\[index\]
    return total / Float64(len(temps))

def main():
    \# ... existing code ...
    
    Add to the end of main() to call the function:


    
          var avg = calculate\_average(temps)
    print(t"Average: {avg}°C")
    
    
=== Conditionals


    Classify the average temperature. Add to the end of main():


    
          if avg \> 25.0:
        print("Status: Hot week")
    elif avg \> 20.0:
        print("Status: Comfortable week")
    else:
        print("Status: Cool week")
    
    
=== Raise errors


    Handle empty data by updating calculate\_average. Now the function can raise an error.


    
      def calculate\_average(temps: List\[Float64\]) raises -\> Float64:
    if len(temps) == 0:  \# Empty list of temperatures
        raise Error("No temperature data")

    var total: Float64 = 0.0
    for index in range(len(temps)):
        total += temps\[index\]
    return total / Float64(len(temps))
    
    What changed:


    - You add raises before the return arrow.
- You add the check for an empty list.
- You raise an Error if it's empty.


    
=== Handle errors


    In main(), wrap your code in try-except for error handling:


    
          try:
        var avg = calculate\_average(temps)
        print(t"Average: {avg}°C")

        if avg \> 25.0:
            print("Status: Hot week")
        elif avg \> 20.0:
            print("Status: Comfortable week")
        else:
            print("Status: Cool week")
    except e:
        print("Error:", e)
    
    To test the error, replace temps with List\[Float64\](). Confirm that your app errors with "No temperature data".


    
=== Python integration


    Add statistics with Python's numpy. First, install it:


    
==== uv


    uv pip install numpy
    
==== pixi


    pixi add numpy
    
==== pip


    pip install numpy
    
==== conda


    conda install numpy
    Then, add the following imports at the top of your file:


    
      from std.python import Python, PythonObject
    
    Now, calculate Python stats at the end of the try block in main():


    
              var np = Python.import\_module("numpy")
        var pytemps: PythonObject = \[20.5, 22.3, 19.8, 25.1\]
        print("Temperature standard deviation:", np.std(pytemps))
    
    
=== Final code


    Your complete analyzer.mojo:


    
      from std.python import Python, PythonObject

def calculate\_average(temps: List\[Float64\]) raises -\> Float64:
    if len(temps) == 0:
        raise Error("No temperature data")

    var total: Float64 = 0.0
    for index in range(len(temps)):
        total += temps\[index\]
    return total / Float64(len(temps))

def main():
    print("Temperature Analyzer")
    var temps: List\[Float64\] = \[20.5, 22.3, 19.8, 25.1\]
    print("Recorded", len(temps), "temperatures")

    for index in range(len(temps)):
        print(t"  Day {index + 1}: {temps\[index\]}°C")

    try:
        var avg = calculate\_average(temps)
        print(t"Average: {avg}°C")

        if avg \> 25.0:
            print("Status: Hot week")
        elif avg \> 20.0:
            print("Status: Comfortable week")
        else:
            print("Status: Cool week")

        var np = Python.import\_module("numpy")
        var pytemps: PythonObject = \[20.5, 22.3, 19.8, 25.1\]
        print("Temperature standard deviation:", np.std(pytemps))
        \_ = pytemps^ \# Allow the Python object to deallocate
    except e:
        print("Error:", e)
    Temperature Analyzer
Recorded 4 temperatures
  Day 1: 20.5°C
  Day 2: 22.3°C
  Day 3: 19.8°C
  Day 4: 25.1°C
Average: 21.924999999999997°C
Status: Comfortable week
Error: No module named 'numpy'
    
=== What you touched


    Mojo variables, lists, loops, functions, conditionals, error handling, and Python integration, all in one working program.


    
=== Use Mojo with AI coding assistants


    If you use AI coding assistants, the mojo-syntax skill keeps you aligned with the latest nightly language releases. Stay up to date with Mojo's rapid development:


    npx skills add modular/skills
    This installs all four #link("https://mojolang.org/docs/tools/skills")[Mojo agent skills], including mojo-syntax.


    
=== Keep going


    #strong[Build something bigger:] Tutorial: Game of Life #strong[Language guide:] #link("https://mojolang.org/docs/manual")[Mojo Manual] #strong[API docs:] #link("https://mojolang.org/docs/std")[Standard Library]