I believe the syntax you were looking for is as follows: import csv with open(‘coors.csv’, mode=”r”) as infile: reader = csv.reader(infile) with open(‘coors_new.csv’, mode=”w”) as outfile: writer = csv.writer(outfile) mydict = {rows[0]:rows[1] for rows in reader} Alternately, for python <= 2.7.1, you want: mydict = dict((rows[0],rows[1]) for rows in reader)
The following are rough guidelines and educated guesses based on experience. You should timeit or profile your concrete use case to get hard numbers, and those numbers may occasionally disagree with the below. A list comprehension is usually a tiny bit faster than the precisely equivalent for loop (that actually builds a list), most likely … Read more
Class scope and list, set or dictionary comprehensions, as well as generator expressions do not mix. The why; or, the official word on this In Python 3, list comprehensions were given a proper scope (local namespace) of their own, to prevent their local variables bleeding over into the surrounding scope (see List comprehension rebinds names … Read more
x if y else z is the syntax for the expression you’re returning for each element. Thus you need: [ x if x%2 else x*100 for x in range(1, 10) ] The confusion arises from the fact you’re using a filter in the first example, but not in the second. In the second example you’re … Read more
list(your_iterator)
The syntax a if b else c is a ternary operator in Python that evaluates to a if the condition b is true – otherwise, it evaluates to c. It can be used in comprehension statements: >>> [a if a else 2 for a in [0,1,0,3]] [2, 1, 2, 3] So for your example, table=””.join(chr(index) … Read more
Use zip(*list): >>> l = [(1,2), (3,4), (8,9)] >>> list(zip(*l)) [(1, 3, 8), (2, 4, 9)] The zip() function pairs up the elements from all inputs, starting with the first values, then the second, etc. By using *l you apply all tuples in l as separate arguments to the zip() function, so zip() pairs up … Read more
From the Python documentation itself, you can use max: >>> mylist = [‘123′,’123456′,’1234’] >>> print max(mylist, key=len) 123456
>>> L = [0, 23, 234, 89, None, 0, 35, 9] >>> [x for x in L if x is not None] [0, 23, 234, 89, 0, 35, 9] Just for fun, here’s how you can adapt filter to do this without using a lambda, (I wouldn’t recommend this code – it’s just for scientific … Read more
Here is how you would do this with a nested list comprehension: [[float(y) for y in x] for x in l] This would give you a list of lists, similar to what you started with except with floats instead of strings. If you want one flat list then you would use [float(y) for x in … Read more