Transcript Lesson 18 Using text files to share data with other programs Python Mini-Course University of Oklahoma Department of Psychology Python Mini-Course: Lesson 18 5/07/09

Lesson 18
Using text files to share data with
other programs
Python Mini-Course
University of Oklahoma
Department of Psychology
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Python Mini-Course: Lesson 18
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Lesson objectives
1. Identify and describe the common
file formats for data exchange,
including text files, csv files, and
tab-delimited files.
2. Read and write delimited text files in
Python
3. Use a spreadsheet to read and
create delimited text files
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Data exchange
 Key principle:
 Data must be stored in a common format
 Industry standard formats for
encoding text
 ASCII, Unicode, etc.
 Industry standard formats for
exchanging data
 Delimited text files
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Delimiting
 Method of marking the
boundaries between data fields in
databases, spreadsheets, and
tabular data
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Common delimited text files
 White-space delimited
 Any non-printable character code
(space, tab, newline, etc)
 Common in older systems and for
numeric data (e.g. SAS data files)
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Common delimited text files
 Comma delimited
 Most common format
 Files are designated as csv files
(comma-separated values)
 Example: USF norms
http://w3.usf.edu/FreeAssociation/
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Common delimited text files
 Tab delimited
 Excellent format for tabular data
 Can be read directly by Excel
 Sometimes called tsv files
 Example: Substance Abuse and
Mental Health Data Archive
http://www.icpsr.com/SAMHDA/index.html
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Example: sqrtable.py
# Create a table of squares and square roots
import math
start, stop, step = 1, 100, 1
delimiter = '\t'
filename = 'squares.txt'
num, sqr, sqr_rt = [], [], []
for val in range(start, stop+1, step):
num.append(val)
sqr.append(val**2)
sqr_rt.append(math.sqrt(val))
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Python Mini-Course: Lesson 18
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Example: sqrtable.py
# Save to a delimited text file
fout = open(filename, 'w')
hdr = 'Num%sSquare%sSqrRoot\n' % (delimiter, delimiter)
print hdr
fout.write(hdr)
for row in zip(num, sqr, sqr_rt):
line = '%d%s%d%s%2.4f\n' % \
(row[0], delimiter, row[1], delimiter, row[2])
print line
fout.write(line)
fout.close()
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Python Mini-Course: Lesson 18
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Exercises
1. Open the file square.txt with a
text editor
2. Open the file square.txt with a
spreadsheet application (e.g.,
Excel)
3. Create a similar spreadsheet
and save as a text file
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Example: readsqr.py
delimiter = '\t'
filename = 'squares.txt'
num, sqr, sqr_rt = [], [], []
fin = open(filename, 'r')
hdr = fin.readline().strip()
for row in fin:
line = row.strip()
entries = line.split(delimiter)
num.append(int(entries[0]))
sqr.append(int(entries[1]))
sqr_rt.append(float(entries[2]))
fin.close()
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Example: readsqr.py
# Print a table of values
print hdr
for row in zip(num, sqr, sqr_rt):
line = '%d%s%d%s%2.4f' % \
(row[0], delimiter, row[1], delimiter, row[2])
print line
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