Boston Python Workshop 3/Friday/Tutorial: Difference between revisions
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* They let us re-use code without having to type it out each time. |
* They let us re-use code without having to type it out each time. |
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* They take input and possibly produce output. You can assign a variable to this output. |
* They take input and possibly produce output. You can assign a variable to this output. |
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* You call a function by using its name followed by the input in parenthesis. |
* You call a function by using its name followed by the input in parenthesis. |
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For example: |
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<pre> |
<pre> |
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<b>Step 1: write a function signature</b> |
<b>Step 1: write a function signature</b> |
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A function signature is the keyword <code>def</code>, a space, the name of your function, an open parenthesis, the comma-separated <b>parameters</b> for your function, a close paranthesis, and a colon. Here's what a function signature looks like for a function that takes no arguments: |
A <b>function signature</b> tells you how the function will be called. It is the keyword <code>def</code>, a space, the name of your function, an open parenthesis, the comma-separated <b>parameters</b> for your function, a close paranthesis, and a colon. Here's what a function signature looks like for a function that takes no arguments: |
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<pre> |
<pre> |
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</pre> |
</pre> |
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Parameters should have names that usefully describe what they are used for in the function. |
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<b>Step 2: do useful work inside the function</b> |
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Underneath the function signature you do your useful work. Everything inside the function is indented, just like with if/else blocks, so Python knows that it is a part of the function. |
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<pre> |
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def add(x, y): |
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result = x + y |
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</pre> |
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<b>Step 3: return something</b> |
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If you want to be able to assign a variable to the output of a function, the function has to <b>return something</b> using the <code>return</code> keyword. |
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<pre> |
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def add(x, y): |
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result = x + y |
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return result |
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</pre> |
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or, even shorter: |
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<pre> |
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def add(x, y): |
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return x + y |
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</pre> |
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Once you define this function, you can use it: |
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<pre> |
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result = add(1234, 5678) |
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print result |
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</pre> |
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Functions don't have to return anything, if you don't want them to. |
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==End of Part 2== |
==End of Part 2== |
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