I am new to python and I am trying to read data from URL. Basically I am reading the historical stock data, get the closing price and save the closing price in to a list. The closing price is available at the 4th index (5th column) of each line. And I want to do all of these within a list comprehension.
Code snippet:
from urllib.request import urlopen
URL = "http://ichart.yahoo.com/table.csv?s=AAPL&a=3&b=1&c=2016&d=9&e=30&f=2016"
def downloadClosingPrice():
urlHandler = urlopen(URL)
next(urlHandler)
return [float(line.split(",")[4]) for line in urlHandler.read().decode("utf8").splitlines() if line]
closingPriceList = downloadClosingPrice()
The above code just works fine. I am able to read and fetch the required data. However just out of curiosity, can the code for list comprehension be written in a more simpler or easier way ?
Thanks...
I did try out various ways and this is how I could do the same using different forms of list comprehension:
return [float(line.decode("utf8").split(",")[4]) for line in urlHandler if line]
# return [float(line.decode("utf8").split(",")[4]) for line in urlHandler.readlines() if line]
# return [float(line.split(",")[4]) for line in urlHandler.read().decode("utf8").splitlines() if line]
The first one is better because it reads the file line by line which saves memory. And of course it's simpler and easier to understand.
Related
I'm trying to reconvert a program that I wrote but getting rid of all for loops.
The original code reads a file with thousands of lines that are structured like:
Ex. 2 lines of a file:
As you can see, the first line starts with LPPD;LEMD and the second line starts with DAAE;LFML. I'm only interested in the very first and second element of each line.
The original code I wrote is:
# Libraries
import sys
from collections import Counter
import collections
from itertools import chain
from collections import defaultdict
import time
# START
# #time=0
start = time.time()
# Defining default program argument
if len(sys.argv)==1:
fileName = "file.txt"
else:
fileName = sys.argv[1]
takeOffAirport = []
landingAirport = []
# Reading file
lines = 0 # Counter for file lines
try:
with open(fileName) as file:
for line in file:
words = line.split(';')
# Relevant data, item1 and item2 from each file line
origin = words[0]
destination = words[1]
# Populating lists
landingAirport.append(destination)
takeOffAirport.append(origin)
lines += 1
except IOError:
print ("\n\033[0;31mIoError: could not open the file:\033[00m %s" %fileName)
airports_dict = defaultdict(list)
# Merge lists into a dictionary key:value
for key, value in chain(Counter(takeOffAirport).items(),
Counter(landingAirport).items()):
# 'AIRPOT_NAME':[num_takeOffs, num_landings]
airports_dict[key].append(value)
# Sum key values and add it as another value
for key, value in airports_dict.items():
#'AIRPOT_NAME':[num_totalMovements, num_takeOffs, num_landings]
airports_dict[key] = [sum(value),value]
# Sort dictionary by the top 10 total movements
airports_dict = sorted(airports_dict.items(),
key=lambda kv:kv[1], reverse=True)[:10]
airports_dict = collections.OrderedDict(airports_dict)
# Print results
print("\nAIRPORT"+ "\t\t#TOTAL_MOVEMENTS"+ "\t#TAKEOFFS"+ "\t#LANDINGS")
for k in airports_dict:
print(k,"\t\t", airports_dict[k][0],
"\t\t\t", airports_dict[k][1][1],
"\t\t", airports_dict[k][1][0])
# #time=1
end = time.time()- start
print("\nAlgorithm execution time: %0.5f" % end)
print("Total number of lines read in the file: %u\n" % lines)
airports_dict.clear
takeOffAirport.clear
landingAirport.clear
My goal is to simplify the program using map, reduce and filter. So far I have sorted teh creation of the two independent lists, one for each first element of each file line and another list with the second element of each file line by using:
# Creates two independent lists with the first and second element from each line
takeOff_Airport = list(map(lambda sub: (sub[0].split(';')[0]), lines))
landing_Airport = list(map(lambda sub: (sub[0].split(';')[1]), lines))
I was hoping to find the way to open the file and achieve the exact same result as the original code by been able to opemn the file thru a map() function, so I could pass each list to the above defined maps; takeOff_Airport and landing_Airport.
So if we have a file as such
line 1
line 2
line 3
line 4
and we do like this
open(file_name).read().split('\n')
we get this
['line 1', 'line 2', 'line 3', 'line 4', '']
Is this what you wanted?
Edit 1
I feel this is somewhat reduntant but since map applies a function to each element of an iterator we will have to have our file name in a list, and we ofcourse define our function
def open_read(file_name):
return open(file_name).read().split('\n')
print(list(map(open_read, ['test.txt'])))
This gets us
>>> [['line 1', 'line 2', 'line 3', 'line 4', '']]
So first off, calling split('\n') on each line is silly; the line is guaranteed to have at most one newline, at the end, and nothing after it, so you'd end up with a bunch of ['all of line', ''] lists. To avoid the empty string, just strip the newline. This won't leave each line wrapped in a list, but frankly, I can't imagine why you'd want a list of one-element lists containing a single string each.
So I'm just going to demonstrate using map+strip to get rid of the newlines, using operator.methodcaller to perform the strip on each line:
from operator import methodcaller
def readFile(fileName):
try:
with open(fileName) as file:
return list(map(methodcaller('strip', '\n'), file))
except IOError:
print ("\n\033[0;31mIoError: could not open the file:\033[00m %s" %fileName)
Sadly, since your file is context managed (a good thing, just inconvenient here), you do have to listify the result; map is lazy, and if you didn't listify before the return, the with statement would close the file, and pulling data from the map object would die with an exception.
To get around that, you can implement it as a trivial generator function, so the generator context keeps the file open until the generator is exhausted (or explicitly closed, or garbage collected):
def readFile(fileName):
try:
with open(fileName) as file:
yield from map(methodcaller('strip', '\n'), file)
except IOError:
print ("\n\033[0;31mIoError: could not open the file:\033[00m %s" %fileName)
yield from will introduce a tiny amount of overhead over directly iterating the map, but not much, and now you don't have to slurp the whole file if you don't want to; the caller can just iterate the result and get a split line on each iteration without pulling the whole file into memory. It does have the slight weakness that opening the file will be done lazily, so you won't see the exception (if there is any) until you begin iterating. This can be worked around, but it's not worth the trouble if you don't really need it.
I'd generally recommend the latter implementation as it gives the caller flexibility. If they want a list anyway, they just wrap the call in list and get the list result (with a tiny amount of overhead). If they don't, they can begin processing faster, and have much lower memory demands.
Mind you, this whole function is fairly odd; replacing IOErrors with prints and (implicitly) returning None is hostile to API consumers (they now have to check return values, and can't actually tell what went wrong). In real code, I'd probably just skip the function and insert:
with open(fileName) as file:
for line in map(methodcaller('strip', '\n'), file)):
# do stuff with line (with newline pre-stripped)
inline in the caller; maybe define split_by_newline = methodcaller('split', '\n') globally to use a friendlier name. It's not that much code, and I can't imagine that this specific behavior is needed in that many independent parts of your file, and inlining it removes the concerns about when the file is opened and closed.
As output of my python code I am getting the marks of Randy and Shaw everytime I run my program. I run this program couple of times every month for many years.
I am storing their marks in a list in python. but how do I save it following format? I am getting output in following format[Output in a row for two different persons]
import pandas
from openpyxl import load_workbook
#These lists I am getting from a very complicated code so just creating new lists here
L1=('7/6/2016', 24,24,13)
L2=('5/8/2016', 25,24,16)
L3=('7/6/2016', 21,16,19)
L4=('5/8/2016', 23,24,21)
L5=('4/11/2016', 13, 12,17)
print('Randy's grades')
print(L1)
print(L2)
print(L3)
print('Shaw's grades')
print(L4)
print(L5)
book = load_workbook('C:/Users/Desktop/Masterfile.xlsx')
writer = pandas.ExcelWriter('Masterfile.xlsx', engine='openpyxl')
Output at run no 1:
For Randy
7/6/2016, 24,24,13
5/8/2016, 25,24,16
For Shaw
7/6/2016, 21,16,19
5/8/2016, 23,24,21
4/11/2016, 13, 12,17
Output at run no 2:
For Randy
7/8/2016, 24,24,13
5/9/2016, 25,24,16
For Shaw
7/8/2016, 21,16,19
5/9/2016, 23,24,21
I will have many such output runs for couple of years so I want to save the data by appending in the same document.
I am using OpenPyxl to open doc and I know I need to use append() operation but I am having hard time to save my list as row. I am new here. Please help me with Syntax!I understand the logic but difficulty with syntax!
Thank you!
Since you said that you are willing to use csv format, I will show a csv solution.
with open('FileToWriteTo.csv', 'w') as outFile:
outFile.write(','.join([str(item) for item in L1])) # Take everything in L1 and put commas between them then write to file
outFile.write('\n') # Write newline
outFile.write(','.join([str(item) for item in L2]))
outFile.write('\n')
outFile.write(','.join([str(item) for item in L3]))
outFile.write('\n')
outFile.write(','.join([str(item) for item in L4]))
outFile.write('\n')
outFile.write(','.join([str(item) for item in L5]))
outFile.write('\n')
If you keep a list of lists instead of separate lists, this becomes easier with a for loop:
with open('FileToWriteTo.csv', 'w') as outFile:
for row in listOfLists:
outFile.write(','.join([str(item) for item in row]))
outFile.write('\n')
I have 2 .csv datasets from the same source. I was attempting to check if any of the items from the first dataset are still present in the second.
#!/usr/bin/python
import csv
import json
import click
#click.group()
def cli(*args, **kwargs):
"""Command line tool to compare and generate a report of item that still persists from one report to the next."""
pass
#click.command(help='Compare the keysets and return a list of keys old keys still active in new keyset.')
#click.option('--inone', '-i', default='keys.csv', help='specify the file of the old keyset')
#click.option('--intwo', '-i2', default='keys2.csv', help='Specify the file of the new keyset')
#click.option('--output', '-o', default='results.json', help='--output, -o, Sets the name of the output.')
def compare(inone, intwo, output):
csvfile = open(inone, 'r')
csvfile2 = open(intwo, 'r')
jsonfile = open(output, 'w')
reader = csv.DictReader(csvfile)
comparator = csv.DictReader(csvfile2)
for line in comparator:
for row in reader:
if row == line:
print('#', end='')
json.dump(row, jsonfile)
jsonfile.write('\n')
print('|', end='')
print('-', end='')
cli.add_command(compare)
if __name__ == '__main__':
cli()
say each csv files has 20 items in it. it will currently iterate 40 times and end when I was expecting it to iterate 400 times and create a report of items remaining.
Everything but the iteration seems to be working. anyone have thoughts on a better approach?
Iterating 40 times sounds just about right - when you iterate through your DictReader, you're essentially iterating through the wrapped file lines, and once you're done iterating it doesn't magically reset to the beginning - the iterator is done.
That means that your code will start iterating over the first item in the comparator (1), then iterate over all items in the reader (20), then get the next line from the comparator(1), then it won't have anything left to iterate over in the reader so it will go to the next comparator line and so on until it loops over the remaining comparator lines (18) - resulting in total of 40 loops.
If you really want to iterate over all of the lines (and memory is not an issue), you can store them as lists and then you get a new iterator whenever you start a for..in loop, so:
reader = list(csv.DictReader(csvfile))
comparator = list(csv.DictReader(csvfile2))
Should give you an instant fix. Alternatively, you can reset your reader 'steam' after the loop with csvfile.seek(0).
That being said, if you're going to compare lines only, and you expect that not many lines will differ, you can load the first line in csv.reader() to get the 'header' and then forgo the csv.DictReader altogether by comparing the lines directly. Then when there is a change you can pop in the line into the csv.reader() to get it properly parsed and then just map it to the headers table to get the var names.
That should be significantly faster on large data sets, plus seeking through the file can give you the benefit of never having the need to store in memory more data than the current I/O buffer.
I am new to python and this is my first practice code with Beautifulsoup. I have not learned creative solutions to specific data extract problems yet.
This program prints just fine but there is some difficult in extracting to the CSV. It takes the first elements but leaves all others behind. I can only guess there might be some whitespace, delimiter, or something that causes the code to halt extraction after initial texts???
I was trying to get the CSV extraction to happen to each item by row but obviously floundered. Thank you for any help and/or advice you can provide.
from urllib.request import urlopen
from bs4 import BeautifulSoup
import csv
price_page = 'http://www.harryrosen.com/footwear/c/boots'
page = urlopen(price_page)
soup = BeautifulSoup(page, 'html.parser')
product_data = soup.findAll('ul', attrs={'class': 'productInfo'})
for item in product_data:
brand_name=item.contents[1].text.strip()
shoe_type=item.contents[3].text.strip()
shoe_price = item.contents[5].text.strip()
print (brand_name)
print (shoe_type)
print (shoe_price)
with open('shoeprice.csv', 'w') as shoe_prices:
writer = csv.writer(shoe_prices)
writer.writerow([brand_name, shoe_type, shoe_price])
Here is one way to approach the problem:
collect the results into a list of dictionaries with a list comprehension
write the results to a CSV file via the csv.DictWriter and a single .writerows() call
The implementation:
data = [{
'brand': item.li.get_text(strip=True),
'type': item('li')[1].get_text(strip=True),
'price': item.find('li', class_='price').get_text(strip=True)
} for item in product_data]
with open('shoeprice.csv', 'w') as f:
writer = csv.DictWriter(f, fieldnames=['brand', 'type', 'price'])
writer.writerows(data)
If you want to also write the CSV headers, add the writer.writeheader() call before the writer.writerows(data).
Note that you could have as well used the regular csv.writer and a list of lists (or tuples), but I like the explicitness and the increased readability of using dictionaries in this case.
Also note that I've improved the locators used in the loop - I don't think using the .contents list and getting product children by indexes is a good and reliable idea.
with open('shoeprice.csv', 'w') as shoe_prices:
writer = csv.writer(shoe_prices)
for item in product_data:
brand_name=item.contents[1].text.strip()
shoe_type=item.contents[3].text.strip()
shoe_price = item.contents[5].text.strip()
print (brand_name, shoe_type, shoe_price, spe='\n')
writer.writerow([brand_name, shoe_type, shoe_price])
Change the open file to the outer loop, so you do not need to open file each loop.
I have a file data.txt containing following lines :
I would like to extract the lines of this file into a list of lists, each line is a list that will be contained within ListOfLines wich is a list of lists.
When there is no data on some cell I just want it to be -1.
I have tried this so far :
from random import randint
ListOfLines=[]
with open("C:\data.txt",'r') as file:
data = file.readlines()
for line in data :
y = line.split()
ListOfLines.append(y)
with open("C:\output.txt",'a') as output:
for x in range(0, 120):
# 'item' represente une ligne
for item in ListOfLines :
item[2] = randint(1, 1000)
for elem in item :
output.write(str(elem))
output.write(' ')
output.write('\n')
output.write('------------------------------------- \n')
How can I improve my program to contain less code and be faster ?
Thank you in advance :)
Well, sharing your sample data in an image don't make easy to working with it. Like this I don't even bother and I assume others do the same.
However, data = file.readlines() forces the content of the file into a list first, and then you iterate through that list. You could do that instantly with 'for line in file:'. That improves it a little.
You haven't mentioned what you want with the otput part which seems quite messy.