Python MiniCourse

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Lesson 18Using text files to share data with
other programs

• Python Mini-Course
• University of Oklahoma
• Department of Psychology

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Lesson objectives

• Identify and describe the common file formats for
  data exchange, including text files, csv files,
  and tab-delimited files.
• Read and write delimited text files in Python
• 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, stop1, step)
• num.append(val)
• sqr.append(val2)
• sqr_rt.append(math.sqrt(val))

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Example sqrtable.py

• Save to a delimited text file
• fout open(filename, 'w')
• hdr 'NumsSquaresSqrRoot\n' (delimiter,
  delimiter)
• print hdr
• fout.write(hdr)
• for row in zip(num, sqr, sqr_rt)
• line 'dsds2.4f\n' \
• (row0, delimiter, row1, delimiter,
  row2)
• print line
• fout.write(line)
• fout.close()

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Exercises

• Open the file square.txt with a text editor
• Open the file square.txt with a spreadsheet
  application (e.g., Excel)
• 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(entries0))
• sqr.append(int(entries1))
• sqr_rt.append(float(entries2))
• 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 'dsds2.4f' \
• (row0, delimiter, row1, delimiter,
  row2)
• print line