Experimenting with Strings (Python)

vegaseat 1 Tallied Votes 324 Views Share

There are some pretty fancy things you can do with strings in Python. You can append, convert, justify, join, split, slice, and list selected files of a folder. I just give you a small sample here.

# a look at strings and methods
# tested with Python23   vegaseat  23jan2005

print "Fill an empty string:"
empty_string = ""
for k in range(65, 91):
  empty_string += chr(k)
print empty_string

print "\nOriginal string (California humor):"
s = "She has 8 body piercings and none are visible"
print s

print "\nSeparate string at any whitespace to a list of words:"
sL = []
sL = s.split()
print sL
print "\nShow item 4 on the list (lists are zero based):"
print sL[4]

# iterate through the list and also show item numbers
print "\nIterate (walk) through the list:"
for k in range (len(sL)):
    print k, sL[k]

# print words and length
print "\nAgain this time show words and ( length ):"
for word in sL:
    print word, " (", len(word), ")"

# append one more word
print "\nAdd one more word to the end:"
print sL

print "\nJoin the list of words to form a string again:"
# single space = " " as a delimiter
print " ".join(sL) + '\n'

# a string can be enclosed in " or ' so if you want to
# use " as part of the string, enclose it with '
s2 = '"How to Serve Your Fellow Man"'
s3 = "Cannibal's recipe book:"

# left justify string s3 and pad with 2 spaces past its length
# then concatenate ( use + ) with string s2
print "Concatenate two strings, leftjustify and pad first string:"
print s3.ljust(len(s3) + 2) + s2 + '\n'

s4 = "hippopotamus"
print "full string  = ", s4

print "spell/space it:"
for char in s4:
  print char,

print "count the characters:"
# create an empty dictionary
charCount = {}
for char in s4:
  charCount[char] = charCount.get(char, 0) + 1
print charCount

print "full string  = ", s4
print "first char   = ", s4[0]
print "last char    = ", s4[-1]
 now for something completely different, slicing ...
 [starting-at-index : but-less-than-index [ : step]]
 start defaults to 0, end to len(sequence), step to 1
print "first 2 char = ", s4[0:2]
print "next 2 char  = ", s4[2:4]
print "last 2 char  = ", s4[-2:]
print "exclude first 3 char  = ", s4[3: ]
print "exclude last 4 char   = ", s4[:-4]
print "reverse the string    = ", s4[::-1]
print "the whole word again  = ", s4
# [start:end:step]
print "spell skipping 2 char = ", s4[::2]

print "concatenate 3 strings = ", s4 + s4 + s4
# same result
print "simply multiply by 3  = ", s4 * 3
# prints 50 dashes
print '-' * 50


print "Convert an integer or float to a string with repr() or str():"
num1 = 3.14
print "num1       =", num1
print "repr(num1) = %s" % repr(num1)
print "str(num1)  = %s" % str(num1)
str1 = str(num1)
print "Convert numeric string back to an integer or float with eval():"
num2 = eval(str1)
print "eval(str1)       =", eval(str1)
print "type(eval(str1)) =", type(eval(str1))
print "If you know the type, you can use int(str1) or float(str1)"
print "An added bonus, function int() has a base option:"
print "binary to decimal int('1111', 2)     =", int('1111', 2)
print "hexadecimal to decimal int('FF', 16) =", int('FF', 16)
print "One more bonus, eval() can evaluate a math expression string:"
print "eval('3 * 4 + 2') =", eval('3 * 4 + 2')


print "Comparing strings:"
print "cmp('mouse', 'mouse') = ", cmp('mouse', 'mouse')
print "cmp('mouse', 'louse') = ", cmp('mouse', 'louse')
print "cmp('louse', 'mouse') = ", cmp('louse', 'mouse')


# make your own words, a little character fun ...
str1 = 'Aack'       # 'Auck' might be a temptation
print "Replace A in %s with other letters:" % str1
# go from B to Z
for b in range(66, 91):
  ch = chr(b)
  if ch == 'Q':     # special case Q, use Qu
    ch = ch + 'u'
  print str1.replace('A', ch)

# how to create a multiline string ...
print "This is a multiline string:"
mlStr = """Noses are running.
Feet are smelling.
Park on driveway.
Drive on parkway.
Recite at a play.
Play at a recital.
print mlStr
print "Show the line that starts with Park:"
# find Park index/position
pos1 = mlStr.find("Park")
# find index of the end of that line
pos2 = mlStr.find("\n", pos1)
# slice the line from the string
line = mlStr[pos1:pos2]
print line


# if you just want to see if a substring is there ...
subStr = 'smell'
if subStr in mlStr:
    print "Found substring '%s'" % subStr


print "There are", mlStr.count('a'), "'a' in the multiline string."
print "They are at index:"
index = mlStr.find('a')  # find first
print index
while index != -1:      # look for more
    index = mlStr.find('a', index + 1)
    if index > 0:
        print index


print "Extract a substring located between two given substrings, here the quotes:"

def extract(text, sub1, sub2):
    """extract a substring between two substrings sub1 and sub2 in text"""
    return text.split(sub1)[-1].split(sub2)[0]

str3 = 'I bought the "Python Cookbook" and could not find one single recipe about cooking the slithery beast!'
# notice that here beginning and trailing spaces can be included with the quotes
str4 = extract(str3, ' "', '" ')
print str3
print str4


print "Line continuation (\) can also be used for long or multiline strings:"
# combining three strings to one string
# (ignores whitespace between strings)
# (do not add a space right behind the \)
str1 = "The alien wheezes, 'Darn, this is it.  I will die now! \n"\
       "Tell my 2.4 million larvae that I esteem them ... \n"\
       "Good-bye, truculent universe.'"
print str1


# file names are strings, so let's find them
# find all the .py files in the working folder (path = '')
import os  # module needed for listdir()
print "Add all the python files in the working folder to a list:"
path = ''
ext  = '.py'
filelist = []
for filename in os.listdir(path):
  if filename.endswith(ext):

# show the list
print filelist

print "\nPrint the file list one item on a line:"
# new line as delimiter
print "\n".join(filelist)


# a function can have a documentation string
def formatDollar(amount):
  "formatDollar(amount) returns a string with the amount formatted to $ currency"
  return "$%.2f" % amount

print "The function's documentation string:"
print formatDollar.__doc__
print "For example", 123.9 * 0.0725,"formatted to", formatDollar(123.9 * 0.0725)
vegaseat 1,735 DaniWeb's Hypocrite Team Colleague

Corrected the mouse/louse mixup, sorry!

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