I have an exercise which I am struggling a lot with related to file handling in python. I tried a lot of times but keep on failing to create the program. Those are the 2 questions.
1) Write a program that takes as input a phrase and a path to a text file on the computer. The program should return either true if the phrase is present in the file or false if the phrase is not present in the file. Can you please help me to figure out those 2 questions. Thanks in advance.
2) Write a program that reads a csv file, where each line contains a coma-separated list of numbers and writes the sum of each line in another file. Use try-catch to handle potential errors such as empty lines or non-numeric values.
For question 1 I wrote:
phrase = input("Enter a phrase: ")
file = open("example.txt", "r")
if phrase in file:
print("True")
else:
print("False")
For question 2 I wrote:
file = open("example.csv", "r")
print(f.readlines())
try:
for i in file:
line = line + 1
file2 = open("lines.csv", "w")
file2.write(line)
file2.close
Related
Firstly, I would like to say that I am newbie in Python.
I will ll try to explain my problem as best as I can.
The main aim of the code is to be able to read, modify and copy a txt file.
In order to do that I would like to split the problem up in three different steps.
1 - Copy the first N lines into a new txt file (CopyFile), exactly as they are in the original file (OrigFile)
2 - Access to a specific line where I want to change a float number for other. I want to append this line to CopyFile.
3 - Copy the rest of the OrigFile from line in point 2 to the end of the file.
At the moment I have been able to do step 1 with next code:
with open("OrigFile.txt") as myfile:
head = [next(myfile) for x iin range(10)] #read first 10 lines of txt file
copy = open("CopyFile.txt", "w") #create a txt file named CopyFile.txt
copy.write("".join(head)) #convert list into str
copy.close #close txt file
For the second step, my idea is to access directly to the txt line I am interested in and recognize the float number I would like to change. Code:
line11 = linecache.getline("OrigFile.txt", 11) #opening and accessing directly to line 11
FltNmb = re.findall("\d+\.\d+", line11) #regular expressions to identify float numbers
My problem comes when I need to change FltNmb for a new one, taking into consideration that I need to specify it inside the line11. How could I achieve that?
Open both files and write each line sequentially while incrementing line counter.
Condition for line 11 to replace the float number. Rest of the lines are written without modifications:
with open("CopyFile.txt", "w") as newfile:
with open("OrigFile.txt") as myfile:
linecounter = 1
for line in myfile:
if linecounter == 11:
newline = re.sub("^(\d+\.\d+)", "<new number>", line)
linecounter += 1
outfile.write(newline)
else:
newfile.write(line)
linecounter += 1
Write a function func(infilepath) that reads the file whose file path is infilepath, and prints the number of times each character(excluding newline characters) appeared in the file, in sorted order of the characters.
Any help would be greatly appreciated !
This won't be the exact answer, but enough to get you started!
First, open a file:
f = open("file.txt", "r")
Then read lines
lines = f.readlines()
Define a dictionary. Split the line by spaces, increment the dictionary by one if they character is already present in the dictionary, else initialize it to 0.
chars = {}
lines = [line.strip() for line in lines]
for line in lines:
line = line.split(" ")
for i in line:
if i not in chars.keys():
chars[i] = 0
else:
chars[i]+=1
More about file handling: https://github.com/thewhitetulip/build-app-with-python-antitextbook/blob/master/manuscript/06-file-handling.md
More about sets/lits/dictionaries: https://github.com/thewhitetulip/build-app-with-python-antitextbook/blob/master/manuscript/04-list-set-dict.md
Some practical examples to get you thinking: https://github.com/thewhitetulip/build-app-with-python-antitextbook/blob/master/manuscript/13-examples.md
So I am completely new to Python and can't figure out what's wrong with my code.
I need to write a program that asks for the name of the existing text file and then of the other one, that doesn't necessarily need to exist. The task of the program is to take content of the first file, convert it to upper-case letters and paste to the second file. Then it should return the number of symbols used in the file(s).
The code is:
file1 = input("The name of the first text file: ")
file2 = input("The name of the second file: ")
f = open(file1)
file1content = f.read()
f.close
f2 = open(file2, "w")
file2content = f2.write(file1content.upper())
f2.close
print("There is ", len(str(file2content)), "symbols in the second file.")
I created two text files to check whether Python performs the operations correctly. Turns out the length of the file(s) is incorrect as there were 18 symbols in my file(s) and Python showed there were 2.
Could you please help me with this one?
Issues I see with your code:
close is a method, so you need to use the () operator otherwise f.close does not do what your think.
It is usually preferred in any case to use the with form of opening a file -- then it is close automatically at the end.
the write method does not return anything, so file2content = f2.write(file1content.upper()) is None
There is no reason the read the entire file contents in; just loop over each line if it is a text file.
(Not tested) but I would write your program like this:
file1 = input("The name of the first text file: ")
file2 = input("The name of the second file: ")
chars=0
with open(file1) as f, open(file2, 'w') as f2:
for line in f:
f2.write(line.upper())
chars+=len(line)
print("There are ", chars, "symbols in the second file.")
input() does not do what you expect, use raw_input() instead.
Can you explain what is going on in this code? I don't seem to understand
how you can open the file and read it line by line instead of all of the sentences at the same time in a for loop. Thanks
Let's say I have these sentences in a document file:
cat:dog:mice
cat1:dog1:mice1
cat2:dog2:mice2
cat3:dog3:mice3
Here is the code:
from sys import argv
filename = input("Please enter the name of a file: ")
f = open(filename,'r')
d1ct = dict()
print("Number of times each animal visited each station:")
print("Animal Id Station 1 Station 2")
for line in f:
if '\n' == line[-1]:
line = line[:-1]
(AnimalId, Timestamp, StationId,) = line.split(':')
key = (AnimalId,StationId,)
if key not in d1ct:
d1ct[key] = 0
d1ct[key] += 1
The magic is at:
for line in f:
if '\n' == line[-1]:
line = line[:-1]
Python file objects are special in that they can be iterated over in a for loop. On each iteration, it retrieves the next line of the file. Because it includes the last character in the line, which could be a newline, it's often useful to check and remove the last character.
As Moshe wrote, open file objects can be iterated. Only, they are not of the file type in Python 3.x (as they were in Python 2.x). If the file object is opened in text mode, then the unit of iteration is one text line including the \n.
You can use line = line.rstrip() to remove the \n plus the trailing withespaces.
If you want to read the content of the file at once (into a multiline string), you can use content = f.read().
There is a minor bug in the code. The open file should always be closed. I means to use f.close() after the for loop. Or you can wrap the open to the newer with construct that will close the file for you -- I suggest to get used to the later approach.
I have this so far but I don't know how to write over the .dat file:
def main():
fname = input("Enter filename:")
infile = open(fname, "r")
data = infile.read()
print(data)
for line in infile.readlines():
score = int(line)
counts[score] = counts[score]+1
infile.close()
total=0
for c in enumerate(counts):
total = total + i*c
average = float(total)/float(sum(counts))
print(average)
main()
Here is my .dat file:
4
3
5
6
7
My statistics professor expects us to learn Python to compute the mean and standard deviation. All I need to know is how to do the mean and then I've got the rest figured out. I want to know how does Python write over each line in a .dat file. Could someone tell me how to fix this code? I've never done programming before.
To answer your question, as I understand it, in three parts:
How to read the file in
in your example you use
infile.read()
which reads the entire contents of the file into a string and takes you to the end of file. Therefore the following
infile.readlines()
will read nothing more. You should omit the first read().
How to compute the mean
There are many ways to do this in python - more or less elegant - and also I guess it depends on exactly what the problem is. But in the simplest case you can just sum and count the values as you go , then divide sum by count at the end to get the result:
infile = open("d.dat", "r")
total = 0.0
count = 0
for line in infile.readlines():
print ("reading in line: ",line)
try:
line_value = float(line)
total += line_value
count += 1
print ("value = ",line_value, "running total =",total, "valid lines read = ",count)
except:
pass #skipping non-numeric lines or characters
infile.close()
The try/except part is just in case you have lines or characters in the file that can't be turned into floats, these will be skipped.
How to write to the .dat file
Finally you seem to be asking how to write the result back out to the d.dat file. Not sure whether you really need to do this, it should be acceptable to just display the result as in the above code. However if you do need to write it back to the same file, just close it after reading from it, reopen it for writing (in 'append' mode so output goes to the end of the file), and output the result using write().
outfile = open("d.dat","a")
outfile.write("\naverage = final total / number of data points = " + str(total/count)+"\n")
outfile.close()
fname = input("Enter filename:")
infile = open(fname, "r")
data = infile.readline() #Reads first line
print(data)
data = infile.readline() #Reads second line
print(data)
You can put this in a loop.
Also, these values will come in as Strings convert them to floats using float(data) each time.
Also, the guys over at StackOverflow are not as bad at math as you think. This could have easily been answered there. (And maybe in a better fashion)