Learning Python – Part 2

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A while back I decided to try and learn Python for the hell of it as it seems like an interesting language and has some of the most concise and user-friendly syntax. Having spent some time going through a number of different learning sources and materials (like the official site python.org which has a very helpful tutorial section) I have put together a set of notes I made as I was learning and hopefully they can be useful to you as a quick list of how-to code snippets.

All the code snapshots I’m showing here are taken from the IDLE Python shell.


To create a new list:



Lists are NOT immutable:



Use the in keyword to check whether an element is in the specified list:



Nesting lists:



The min and max functions:



The list function – you can use the list() function to convert a tuple to a list:



Element values of a tuple cannot be changed and tuple elements are put between parenthesis instead of square bracket:



Deleting an item from list:


or you can use the remove() function:



Replace portion of list with slicing:



Insert a list into another list with slicing:



Delete a portion of list with slicing:



Appending to a list by using simple concatenation:


or use append or extend, the difference being append adds a single element to the list where as extend works like the concatenation above.


now compare this to extend:



Like in Javascript, you can use a list like a stack (FILO) too:



You can also use a list as a queue (FIFO) using the collections.deque function:



Sorting a list:


you can do the same to a string too using the sorted function:



To construct an empty tuple:


To construct a tuple with a single item:



You can unpack a tuple or list (like the pattern matching in F#):




There must be the same number of elements on the left as the tuple on the right:



Use the range() function to generate a range of integers:



Use the filter() function to filter a list:



Use the map() function to project a sequence’s items to something else:


you can also use it like the zip() method in F# by passing in multiple sequences:


if the lists are not of equal length, None is used to fill in the gap:



Use the reduce() function to return a single value from a list of element, e.g. to sum the numbers 1-4:


you can also pass in a third argument to indicate the starting value of the accumulator:



You can remove an item from a list using its index with the del statement:


note that del statement doesn’t return any values.

You can also use it to delete the entire list or part of the list:


or to delete the variable itself:



List comprehensions (similar to those in F#):



If the result is a tuple, then it must be parenthesized:



You can add additional filters:



Or you can have a loop inside another loop:



Nested List Comprehensions, e.g. to turn the columns of a matrix into rows:


remember, read nested comprehensions from right to left!

Nested comprehensions is a powerful tool but adds complexity, where possible, use built-in functions. E.g. the above can be done using zip():



When looping through a sequence, the position index and corresponding value can be retrieved at the same time using the enumerate() function:



You can also use zip() function to loop over two or more sequences at the same time:


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Hi, I’m Yan. I’m an AWS Serverless Hero and I help companies go faster for less by adopting serverless technologies successfully.

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