Join Michele Vallisneri for an in-depth discussion in this video Comprehensions, part of Python: Data Analysis.
- In Python programming,…especially when you're dealing with data,…there are many cases where you want to iterate…over list or dict, perform an operation on every element,…and then collect all the results in a new list or dict.…You can certainly do that with a For Loop,…but Python offers a great feature, comprehensions,…that lets you write shorter and clearer code…that achieves the same effect.…In this movie, we're going to review…how to write loops as comprehensions,…how to apply them only to select items,…and how to do the same for lists and for dicts.…
We're now going to open the exercise file for this movie.…If you're already in the IPython notebook,…you can just go to the finder interface…and select the correct file.…Let's look again at the scenario…where we need comprehensions.…Say for instance that we're building a list of squares.…I'm going to start with an empty list, just empty brackets,…and then keep appending to it throughout the loop.…The result is the list that I desired.…
A list comprehension achieves this in a single line…
- Writing and running Python in iPython
- Using Python lists and dictionaries
- Creating NumPy arrays
- Indexing and slicing in NumPy
- Downloading and parsing data files into NumPy and Pandas
- Using multilevel series in Pandas
- Aggregating data in Pandas
Skill Level Intermediate
Q: The course shows how to download files from FTP and web servers using Python 3.X. How do I do the same thing with Python 2.7?
A: First import urllib, then use urllib.urlretrieve(URL,filename). For instance, to download the stations.txt files used in the chapter 5 video “Downloading and parsing data files,” you’d do urllib.urlretrieve(‘ftp://ftp.ncdc.noaa.gov/pub/data/ghcn/daily/ghcnd-stations.txt','stations.txt').
1. Installation and Setup
2. Refresher: Data Containers in Python
3. Word Anagrams in Python
4. Introduction to NumPy
5. Weather Data with NumPy
6. Introduction to Pandas
7. Baby Names with Pandas
Next steps1m 36s
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