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Boston Python Workshop 7/Friday/Tutorial: Difference between revisions
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, 11 years ago→End of Part 2
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<pre>
print "I'm a happy camper"
</pre>▼
<pre>▼
</pre>
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c = "fox jumps over the lazy dog"
print "The " + a * 3 + " " + b * 3 + " " + c
</pre>▼
<pre>▼
</pre>
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That was our first multi-line piece of code, and the way to enter it at a Python prompt is a little different. First, type the
<code> if 6 > 5:</code>
part, and
<code> ...</code>
as a prompt, instead of the usual <code>>>></code>. This is Python telling us that we are in the middle of a <b>code block</b>, and so long as we indent our code it should be a part of this code block.
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Enter 4 spaces, and then type
<code> print "Six is greater than five!"</code>
<pre>
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====more choices: <code>if</code> and <code>else</code>====
You can use the <code>else</code> keyword to execute code
<pre>
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<b>Remember that '=' is for assignment and '==' is for comparison.</b>
====In summary: the structure of if/elif/else====
Here's a diagram of <code>if/elif/else</code>:
[[File:If-elif-else.png]]
Do you understand the difference between <code>elif</code> and <code>else</code>? When do you indent? When do you use a colon? If you're not sure, talk about it with a neighbor or staff member.
==Writing Functions==
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<b>Step 1: write a function signature</b>
A <b>function signature</b> tells you how the function will be called. It starts with the keyword <code>def</code>, which tells Python that you are defining a function. Then comes a space, the name of your function, an open parenthesis, the comma-separated input <b>
<code>def myFunction():</code>
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<code>def myFunction(myList, myInteger):</code>
<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.
You can use the variables passed into the function as
<pre>
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Functions don't have to return anything, if you don't want them to. They usually return something because we usually want to be able to assign variables to their output.
====What is the difference between <code>print</code> and <code>return</code>?====
Think for a moment about the differences between <code>print</code> and <code>return</code>:
* <code>print</code> prints output to the screen so your eyes can see it.
* <code>return</code> is used to hand off a value from inside a function to a variable outside the function.
For example:
▲<pre>
def add(x, y):
print x + y
▲</pre>
will print <code>x + y</code> to the screen so your eyes can see it.
▲<pre>
def add(x, y):
return x + y
▲</pre>
will hand off <code>x + y</code> from inside the function to outside the function. This allows you to do something like:
<pre>
result = add(5, 6)
print result
</pre>
Does that make sense? If not, talk about it with a neighbor or staff member.
==End of Part 2==
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