Am trying to check if elements of a list match elements of another. But there is a slight twist to the problem.
alist = ['949', '714']
blist = ['(714)824-1234', '(419)312-8732', '(949)555-1234', '(661)949-2867']
Am trying to match the elements of alist to the blist, but only the area code part(in blist). Here is my current code:
def match_area_codes(alist, blist):
clist =[]
for i in alist:
for j in blist:
if i in j:
clist.append(j)
return clist
The code works for the most part, except when there is a string matching the area code anywhere else in the list. It should only print:
['(714)824-1234', '(949)555-1234']
but it ends up printing
['(714)824-1234', '(949)555-1234', '(661)949-2867']
as there is a '949' in the last phone number. Is there a way to fix this?
You can use a regular expression to get the part within (...) and compare that part to alist.
import re
def match_area_codes(alist, blist):
p = re.compile(r"\((\d+)\)")
return [b for b in blist if p.search(b).group(1) in alist]
Example:
>>> alist = set(['949', '714'])
>>> blist = ['(714)824-1234', '(419)312-8732', '(949)555-1234', '(661)949-2867']
>>> match_area_codes(alist, blist)
['(714)824-1234', '(949)555-1234']
If you really really want to do it without regular expressions, you could, e.g., find the position of the ( and ) and thus get the slice from the string corresponding to the region code.
def match_area_codes(alist, blist):
find_code = lambda s: s[s.index("(") + 1 : s.index(")")]
return [b for b in blist if find_code(b) in alist]
However, I would strongly suggest to just take this as an opportunity for getting started with regular expressions. It's not all that hard, and definitely worth it!
Related
Provided with a list of lists. Here's an example myList =[[70,83,90],[19,25,30]], return a list of lists which contains the difference between the elements. An example of the result would be[[13,7],[6,5]]. The absolute value of (70-83), (83-90), (19-25), and (25-30) is what is returned. I'm not sure how to iterate through the list to subtract adjacent elements without already knowing the length of the list. So far I have just separated the list of lists into two separate lists.
list_one = myList[0]
list_two = myList[1]
Please let me know what you would recommend, thank you!
A custom generator can return two adjacent items at a time from a sequence without knowing the length:
def two(sequence):
i = iter(sequence)
a = next(i)
for b in i:
yield a,b
a = b
original = [[70,83,90],[19,25,30]]
result = [[abs(a-b) for a,b in two(sequence)]
for sequence in original]
print(result)
[[13, 7], [6, 5]]
Well, for each list, you can simply get its number of elements like this:
res = []
for my_list in list_of_lists:
res.append([])
for i in range(len(my_list) - 1):
# Do some stuff
You can then add the results you want to res[-1].
Can someone explain the last line of this Python code snippet to me?
Cell is just another class. I don't understand how the for loop is being used to store Cell objects into the Column object.
class Column(object):
def __init__(self, region, srcPos, pos):
self.region = region
self.cells = [Cell(self, i) for i in xrange(region.cellsPerCol)] #Please explain this line.
The line of code you are asking about is using list comprehension to create a list and assign the data collected in this list to self.cells. It is equivalent to
self.cells = []
for i in xrange(region.cellsPerCol):
self.cells.append(Cell(self, i))
Explanation:
To best explain how this works, a few simple examples might be instructive in helping you understand the code you have. If you are going to continue working with Python code, you will come across list comprehension again, and you may want to use it yourself.
Note, in the example below, both code segments are equivalent in that they create a list of values stored in list myList.
For instance:
myList = []
for i in range(10):
myList.append(i)
is equivalent to
myList = [i for i in range(10)]
List comprehensions can be more complex too, so for instance if you had some condition that determined if values should go into a list you could also express this with list comprehension.
This example only collects even numbered values in the list:
myList = []
for i in range(10):
if i%2 == 0: # could be written as "if not i%2" more tersely
myList.append(i)
and the equivalent list comprehension:
myList = [i for i in range(10) if i%2 == 0]
Two final notes:
You can have "nested" list comrehensions, but they quickly become hard to comprehend :)
List comprehension will run faster than the equivalent for-loop, and therefore is often a favorite with regular Python programmers who are concerned about efficiency.
Ok, one last example showing that you can also apply functions to the items you are iterating over in the list. This uses float() to convert a list of strings to float values:
data = ['3', '7.4', '8.2']
new_data = [float(n) for n in data]
gives:
new_data
[3.0, 7.4, 8.2]
It is the same as if you did this:
def __init__(self, region, srcPos, pos):
self.region = region
self.cells = []
for i in xrange(region.cellsPerCol):
self.cells.append(Cell(self, i))
This is called a list comprehension.
I'm trying to change characters from x into upper or lower character depending whether they are in r or c. And the problem is that i can't get all the changed characters into one string.
import unittest
def fun_exercise_6(x):
y = []
r = 'abcdefghijkl'
c = 'mnopqrstuvwxz'
for i in range(len(x)):
if(x[i] in r):
y += x[i].lower()
elif(x[i] in c):
y += x[i].upper()
return y
class TestAssignment1(unittest.TestCase):
def test1_exercise_6(self):
self.assertTrue(fun_exercise_6("osso") == "OSSO")
def test2_exercise_6(self):
self.assertTrue(fun_exercise_6("goat") == "gOaT")
def test3_exercise_6(self):
self.assertTrue(fun_exercise_6("bag") == "bag")
def test4_exercise_6(self):
self.assertTrue(fun_exercise_6("boat") == "bOaT" )
if __name__ == '__main__':
unittest.main()
Using a list as you are using is probably the best approach while you are figuring out whether or not each character should be uppered or lowered. You can join your list using str's join method. In your case, you could have your return statement look like this:
return ''.join(y)
What this would do is join a collection of strings (your individual characters into one new string using the string you join on ('').
For example, ''.join(['a', 'b', 'c']) will turn into 'abc'
This is a much better solution than making y a string as strings are immutable data types. If you make y a string when you are constructing it, you would have to redefine and reallocate the ENTIRE string each time you appended a character. Using a list, as you are doing, and joining it at the end would allow you to accumulate the characters and then join them all at once, which is comparatively very efficient.
If you define y as an empty string y = "" instead of an empty list you will get y as one string. Since when you declare y = [] and add an item to the list, you add a string to a list of string not a character to a string.
You can't compare a list and a string.
"abc" == ["a", "b", "c'] # False
The initial value of y in the fun_exercise_6 function must be ""
I have a list of data from which I need to extract the indices of some strings within that list:
str=['cat','monkey']
list=['a cat','a dog','a cow','a lot of monkeys']
I've been using re.compile to match (even partial match) individual elements of the str list to the list:
regex=re.compile(".*(monkey).*")
b=[m.group(0) for l in list for m in [regex.search(l)] if m]
>>> list.index(b[0])
3
However, when I try to iterate over the str list to find the indices of those elements, I obtain empty lists:
>>> for i in str:
... regex=re.compile(".*(i).*")
... b=[m.group(0) for l in list for m in [regex.search(l)] if m]
... print(b)
...
[]
[]
I imagine that the problem is with regex=re.compile(".*(i).*"), but I don't know how to pass the ith element as a string.
Any suggestion is very welcome, thanks!!
It looks like you need to use string formatting.
for i in str:
match_pattern = ".*({}).*".format(i)
regex = re.compile(match_pattern)
b = [m.group(0) for l in list for m in [regex.search(l)] if m]
print(b)
I can use this to figure out what the longest string in the sequence is but how exactly can I find the index of the longest string. New to python btw, go easy on my pls.
def longest_string(seq):
max_list = max(seq,key=len)
return max_list
print(longest_string(["h","el","lo","worl","d"]))
worl
Instead of checking the length only, use the enumerate method to get the position as well:
>>> seq = ["h","el","lo","worl","d"]
>>> max(enumerate(seq), key=lambda x: len(x[1]))
(3, 'worl')
Then you can just return the first item of the tuple.
>>> seq = ["h","el","lo","worl","d"]
>>> seq.index(max(seq))
3