What is Python?¶

Python is a dynamic, strongly typed, object-oriented programming language.

In [2]:

from IPython.display import Image
Image(filename='confused-cat.jpg')

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Courtesy of flicky user sfroehlich1121.

Before we go into what the above means, note that there is a strong, and growing, Python community in Astronomy - for instance

X-ray astronomy (CIAO)
optical/ground-based astronomy (PyRAF)
radio (CASA)
Solar astronomy (SunPy)

It's also a useful "transfereable" skill, for those of you that end up moving out of Astronomy.

Once you've got the hang of Python - and found out that many questions you have have already been answered on Stack Overflow - the trick is in finding the package you need, rather than writing your own code. cough cough astropy cough cough

You should also be aware of R - The R project for Statistical Computing - which is not Python, but is important as Astronomy moves into the era of

In [4]:

Image(filename='big_data.png')

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courtesy of the internetz.

Dy·nam·ic¶

always active or changing
having or showing a lot of energy
of or relating to energy, motion, or physical force

At least that's what Merriam-Webster says.

In [1]:

a = 23
print("The answer is " + str(a))
b = a + len("confused kitty is confused")
print("The answer is now " + str(b))
a = "Goooooooooooooollllll"
print("The answer is now " + a)

The answer is 23
The answer is now 49
The answer is now Goooooooooooooollllll

Things to note:

you can define variables when you need them
you do not need to define the "type" of a variable
you can change what you store in a variable (one moment it's an integer, then it's a string)

Strongly typed¶

The operations you can do depend on the "type" of the variable (or constant).

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len("This is a string")

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In [3]:

len(23)

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-3-c9328ce85f6c> in <module>()
----> 1 len(23)

TypeError: object of type 'int' has no len()

Aside¶

These error messages look confusing at first, but you will quickly learn what to look for: ignore everything until the last line!

On the last line you'll see "BlahError: hopefully something more informative than blah", which tells you the type of error (so in this case, it is a "TypeError"), and then an optional string giving more information, which in this case says that you have tried to use len on something that doesn't have a length.

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