I am reading in a csv file and then trying to separate the header from the rest of the file.
hn variable is is the read-in file without the first line.
hn_header is supposed to be the first row in the dataset.
If I define just one of these two variables, the code works. If I define both of them, then the one written later does not contain any data. How is that possible?
from csv import reader
opened_file = open("hacker_news.csv")
read_file = reader(opened_file)
hn = list(read_file)[1:] #this should contain all rows except the header
hn_header = list(read_file)[0] # this should be the header
print(hn[:5]) #works
print(len(hn_header)) #empty list, does not contain the header
The CSV reader can only iterate through the file once, which it does the first time you convert it to a list. To avoid needing to iterate through multiple times, you can save the list to a variable.
hn_list = list(read_file)
hn = hn_list[1:]
hn_header = hn_list[0]
Or you can split up the file using extended iterable unpacking
hn_header, *hn = list(read_file)
Just change below line in your code, no additional steps needed. read_file = list(reader(opened_file)). I hope now your code is running perfectly.
The reader object is an iterator, and by definition iterator objects can only be used once. When they're done iterating you don't get any more out of them.
You can refer more about from this Why can I only use a reader object once? question and also above block-quote taken from that question.
Related
I am reading a text file and I want to read a list of tuples so that I can add another tuple to it in my program and write that appended tuple back to the text file.
Example in the file
[('john', 'abc')]
Want to write back to the file as
[('john', 'abc'), ('jack', 'def')]
However, I whenever I keep writing back to the file, the appended tuple seems to add in double quotes along with square brackets. I just want it to appear as above.
You can write a reusable function which takes 2 parameters file_path (on which you want to write tuple), tup (which you want to append) and put your logic inside that. Later you can supply proper data to this function and it will do the job for you.
Note: Don't forget to read the documentation as comments in code
tuples.txt (Before writing)
[('john', 'abc')]
Code
def add_tuple_to_file(file_path, tup):
with open(file_path, 'r+') as f:
content = f.read().strip() # read content from file and remove whitespaces around
tuples = eval(content) # convert string format tuple to original tuple object (not possible using json.loads())
tuples.append(tup) # append new tuple `tup` to the old list
f.seek(0) # After reading file, file pointer reaches to end of file so place it again at beginning
f.truncate() # truncate file (erase old content)
f.write(str(tuples)) # write back the updated list
# Try
add_tuple_to_file("./tuples.txt", ('jack', 'def'))
tuples.txt (After writing back)
[('john', 'abc'), ('jack', 'def')]
References
https://www.geeksforgeeks.org/python-ways-to-convert-string-to-json-object/
How to open a file for both reading and writing?
You can use ast.literal_eval to get the list object from the string.
import ast
s = "[('john', 'abc')]"
o = ast.literal_eval(s)
print(repr(o)==s)
o.append(('jack', 'def'))
newstr = repr(o)
print(newstr)
Here it is in action.
I have this in csv file:
Titre,a,b,c,d,e
01,jean,paul,,
01,,,jack,
02,jeanne,jack,,
02,,,jean
and i want :
Titre,a,b,c,d,e
01,jean,paul,jack,
02,jeanne,jack,,jean
can you help me ?
In general, a good approach is to read the csv file and iterate through the rows using Python's CSV module.
CSV will create an iterator that will let you loop through your file like this:
import csv
with open('your filename.csv', 'r') as infile:
reader = csv.reader(infile)
for line in reader:
for value in line:
# Do your thing
You're going to need to construct a new data set that has different properties. The requirements you described:
Ignore any empty cells
Any time you encounter a row that has a new index number, add a new row to your new data set
Any time you encounter a row that has an index number you've seen before, add it to the row that you already created (except for that index number value itself)
I'm not writing that part of the code for you because you need to learn and grow. It's a good task for a beginner.
Once you've constructed that data set, it will look like this:
example_processed_data = [["Titre","a","b","c","d","e"],
["01","jean","paul","jack"],
["02","jeanne","jack","","jean"]]
You can then create a CSV writer, and create your outfile by iterating over that data, similarly to how you iterated over the infile:
with open('outfile.csv', 'w') as outfile:
writer = csv.writer(outfile)
for line in example_processed_data:
writer.writerow(line)
print("Done! Wrote", len(example_processed_data), "lines to outfile.csv.")
I am trying to automate the production of pdfs by reading data from a pandas data frame and writing it a page on an existing pdf form using pyPDF2 and reportlab. The main meat of the program is here:
def pdfOperations(row, bp):
packet = io.BytesIO()
can = canvas.Canvas(packet, pagesize=letter)
createText(row, can)
packet.seek(0)
new_pdf = PdfFileReader(packet)
textPage = new_pdf.getPage(0)
secondPage = bp.getPage(1)
secondPage.mergePage(textPage)
assemblePDF(frontPage, secondPage, row)
del packet, can, new_pdf, textPage, secondPage
def main():
df = openData()
bp = readPDF()
frontPage = bp.getPage(0)
for ind in df.index:
row = df.loc[ind]
pdfOperations(row, bp)
This works fine for the first row of data and the first pdf generated, but for the subsequent ones all the text is overwritten. I.e. the second pdf contains text from the first iteration and the second. I thought the garbage collection would take care of all the in memory changes, but that does not seem to be happening. Anyone know why?
I even tries forcing the objects to be deleted after the function has run its course, but no luck...
You read bp only once before the loop. Then in the loop, you obtain its second page via getPage(1) and merge stuff to it. But since its always from the same object (bp), each iteration will merge to the same page, therefore all the merges done before add up.
While I don't find any way to create a "deepcopy" of a page in PyPDF2's docs, it should work to just create a new bp object for each iteration.
Somewhere in readPDF you must have done something where you open your template PDF into a binary stream and then pass that to PdfFileReader. Instead, you could read the data into a variable:
with open(filename, "rb") as f:
bp_bin = f.read()
And from that, create a new PdfFileReader instance for each loop iteration:
for ind in df.index:
row = df.loc[ind]
bp = PdfFileReader(bp_bin)
pdfOperations(row, bp)
This should "reset" the secondPage everytime without any additional file I/O overhead. Only the parsing is done again each time, but depending on the file size and contents, maybe the time that takes is low and you can live with that.
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'm having some troubles processing some input.
I am reading data from a log file and store the different values according to the name.
So my input string consists of ip, name, time and a data value.
A log line looks like this and it has \t spacing:
134.51.239.54 Steven 2015-01-01 06:09:01 5423
I'm reading in the values using this code:
loglines = file.splitlines()
data_fields = loglines[0] # IP NAME DATE DATA
for loglines in loglines[1:]:
items = loglines.split("\t")
ip = items[0]
name = items[1]
date = items[2]
data = items[3]
This works quite well but I need to extract all names to a list but I haven't found a functioning solution.
When i use print name i get:
Steven
Max
Paul
I do need a list of the names like this:
['Steven', 'Max', 'Paul',...]
There is probably a simple solution and i haven't figured it out yet, but can anybody help?
Thanks
Just create an empty list and add the names as you loop through the file.
Also note that if that file is very large, file.splitlines() is probably not the best idea, as it reads the entire file into memory -- and then you basically copy all of that by doing loglines[1:]. Better use the file object itself as an iterator. And don't use file as a variable name, as it shadows the type.
with open("some_file.log") as the_file:
data_fields = next(the_file) # consumes first line
all_the_names = [] # this will hold the names
for line in the_file: # loops over the rest
items = line.split("\t")
ip, name, date, data = items # you can put all this in one line
all_the_names.append(name) # add the name to the list of names
Alternatively, you could use zip and map to put it all into one expression (using that loglines data), but you rather shouldn't do that... zip(*map(lambda s: s.split('\t'), loglines[1:]))[1]