Editing Community Data Science Course (Spring 2016)/Day 1 Tutorial (section)

===String Concatenation===

You can smoosh strings together (called "concatenation") using the '+' sign:

 "Hello" + "World"

 name = "Jessica"
 "Hello " + name

How about concatenating different data types?

 "Hello" + 1

Hey now! The output from the previous example was really different and interesting; let's break down exactly what happened:

<code>>>> "Hello" + 1</code><br />
<code>Traceback (most recent call last):</code><br />
<code>  File "<stdin>", line 1, in <module></code><br />
<code>TypeError: cannot concatenate 'str' and 'int' objects</code>

Python is giving us a '''traceback'''. A traceback is details on what was happening when Python encountered an Exception or Error -- something it doesn't know how to handle.

There are many kinds of Python errors, with descriptive names to help us humans understand what went wrong. In this case we are getting a <code>TypeError</code>: we tried to do some operation on a data type that isn't supported for that data type.

Python gives us a helpful error message as part of the TypeError:

<code>"cannot concatenate 'str' and 'int' objects"</code>

We saw above the we can concatenate strings:

 "Hello" + "World"

works just fine.

However,

 "Hello" + 1

produces a <code>TypeError</code>. We are telling Python to concatenate a string and an integer, and that's not something Python understands how to do.

We can convert an integer into a string ourselves, using the <code>str</code> function:

 "Hello" + str(1)

Like the <code>type</code> function from before, the <code>str</code> function takes 1 argument. In the above example it took the integer 1. <code>str</code> takes a Python object as input and produces a string version of that input as output.