Transcript PythonFileI/O

File I/O
Dr. Nancy Warter-Perez
Homework Submission Guidelines
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Submit your programs via Email
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[email protected]
Subject template for HWx: Chem434 HWx or Binf400 HWx
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Example for HW1P: Chem434 HW1P or Binf400 HW1P
Email sample output (screen shot(s)) to show that your
program is working properly
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Homework Due Dates
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Programming Homework Dues Dates are somewhat flexible because
of the diverse programming skills of students in the class.
Always submit your homework on the due date. If the
program is not working, also submit an explanation of
where the problem is. If the program is working, submit
screen shots that demonstrate your program is working
properly.
You have up to one week to resubmit your homework
(with no penalty) after the due date. Follow the same
guidelines (i.e., if working submit screen shots and if not
working, submit explanation (and screen shots if possible).
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File Inputs and Outputs (I/O)
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Data can be read directly from a file and
results can be written directly to a file.
First you need to open the file:
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Output Ex: outfile = open("out.txt", 'w')
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'w' indicates that the file will be written to by the script
(i.e., it is an output file)
The file out.txt will be created by the script in the same
directory as your script
The variable outfile will allow you to refer to the out.txt
file in your program. You can use any variable name you
want.
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File Inputs and Outputs (I/O)
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Another example of opening a file:
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Input Ex: infile = open("D:\\Docs\\test.txt", 'r')
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'r' indicates that the file will be read by the script (i.e., it
is and input file)
The file test.txt should already exist in the folder
specified
Notice that here the exact path of where to find the file
is given (" D:\\Docs\\test.txt")
The variable infile will allow you to refer to test.txt file
in your program. You can use any variable name that
you want.
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File Inputs and Outputs (I/O)
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Second, after opening the file you can either
read or write to it.
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Input Ex:
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s = infile.read()
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The entire contents of the input file (test.txt) will be read
in as a string and stored in s.
Refer to slide 9 for more input file operations.
Output Ex:
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outfile.write(str)
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This will write the contents of the string variable (str) into
the file (out.txt)
Refer to slide 10 for more output file operations.
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File Inputs and Outputs (I/O)
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Third, after you are done with the file,
close it so that other applications can
access the file.
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Input Ex:
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infile.close()
Output Ex:
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outfile.close()
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Common input file operations
Operation
input = open ('file', 'r')
S = input.read()
S = input.read(N)
S = input.readline()
L = input.readlines()
Interpretation
open input file
read entire file into
string S
Read N bytes (N>= 1)
Read next line
Read entire file into list
of line strings
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Common output file operations
Operation
Interpretation
output = open('file', 'w') create output file
output.write(S)
Write string S into file
output.writelines(L)
Write all line strings in
list L into file
output.close()
Manual close (good
habit)
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Example
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Write a script to read in a string of integer
numbers from a file, convert each character
(‘0’ to ‘9’) to an integer, and store it into an
output file
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Example Python Script
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Example file I/O script
Script will read in an input string of numbers from an input file,
convert each character to an integer and write the converted
values to an output file.
Written by: Prof. Nancy Warter-Perez
Date created: May 5, 2009
infile = open("input.txt", "r") # before running the script, create input.txt with a string of characters
outfile = open("output.txt", "w") # will be created by the program.
s = infile.read() #read in entire file into s (note, there are other options for reading files)
infile.close() #done reading the file
for c in s:
outfile.write("%s," % int(c)) #writes each value to the output file separated by comma
outfile.close()
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Example input and output files
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Contents of input.txt before (and after)
running the script
 1234567898765456789
Contents of output.csv after running the
script
 1,2,3,4,5,6,7,8,9,8,7,6,5,4,5,6,7,8,9,
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Plot using Excel
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In Excel, open the output.txt file (as a text file)
Choose delimited data type and select comma as a
delimiter
Select the row of data
Select the output graph format
Example:
10
9
8
7
6
5
Series1
4
3
2
1
0
1
2
3
4
5
6
7
8
9
10 11 12 13 14 15 16 17 18 19
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