6.1 Strings as sequences


>>> x = "Hello"
>>> x[0]
'H'
>>> x[-1]
'o'
>>> x[1:]
'ello'

>>> x = "Goodbye\n"
>>> x = x[:-1]
>>> x
'Goodbye'

>>> len("Goodbye")
7

6.2 Basic String Operations

>>> x = "Hello " + "World"
>>> x
'Hello World'

>>> 8 * "x"
'xxxxxxxx'

6.2 Escape sequences

>>> 'm'
'm'
>>> '\155'
'm'
>>> '\x6D'
'm'

>>> '\n'
'\n'
>>> '\012'
'\n'
>>> '\x0A'
'\n'

>>> unicode_a ='\N{LATIN SMALL LETTER A}'
>>> unicode_a
'a'
>>> unicode_a_with_acute = '\N{LATIN SMALL LETTER A WITH ACUTE}'
>>> unicode_a_with_acute
'á'
>>> "\u00E1"
'á'
>>>

6.2 Evaluating special characters

>>> 'a\n\tb'
'a\n\tb'
>>> print('a\n\tb')
a
	b

>>> print("abc\n")
abc

>>> print("abc\n", end="")           
abc
>>>
6.4.1 split and join

>>> " ".join(["join", "puts", "spaces", "between", "elements"])
'join puts spaces between elements'

>>> "::".join(["Separated", "with", "colons"])
'Separated::with::colons'

>>> "".join(["Separated", "by", "nothing"])
'Separatedbynothing'

>>> x = "You\t\t can have tabs\t\n \t and newlines \n\n " \
               "mixed in"
>>> x.split()
['You', 'can', 'have', 'tabs', 'and', 'newlines', 'mixed', 'in']
>>> x = "Mississippi"
>>> x.split("ss")
['Mi', 'i', 'ippi']

>>> x = 'a b c d'
>>> x.split(' ', 1)
['a', 'b c d']
>>> x.split(' ', 2)
['a', 'b', 'c d']
>>> x.split(' ', 9)
['a', 'b', 'c', 'd']


6.4.1 converting to numbers

>>> float('123.456')
123.456
>>> float('xxyy') 
Traceback (innermost last):
 File "<stdin>", line 1, in ?
ValueError: invalid literal for float(): xxyy
>>> int('3333')
3333
>>> int('123.456')
Traceback (innermost last):
 File "<stdin>", line 1, in ?
ValueError: invalid literal for int() with base 10: 123.456
>>> int('10000', 8)
4096
>>> int('101', 2)
5
>>> int('ff', 16)
255
>>> int('123456', 6)
Traceback (innermost last):
 File "<stdin>", line 1, in ?
ValueError: invalid literal for int()with base 6: 123456


6.4.3 Getting rid of whitespace

>>> x = "  Hello,    World\t\t "
>>> x.strip()
'Hello,    World'
>>> x.lstrip()
'Hello,    World\t\t '
>>> x.rstrip()
'  Hello,    World'

>>> import string
>>> string.whitespace
' \t\n\r\x0b\x0c'
>>> " \t\n\r\v\f"
' \t\n\r\x0b\x0c'

>>> x = "www.python.org"
>>> x.strip("w")
'.python.org'
>>> x.strip("gor")
'www.python.'
>>> x.strip(".gorw")
'python'


6.4.4 Searching

>>> x = "Mississippi"
>>> x.find("ss")
2
>>> x.find("zz")
-1

>>> x = "Mississippi"
>>> x.find("ss", 3)
5
>>> x.find("ss", 0, 3)
-1

>>> x = "Mississippi"
>>> x.rfind("ss")
5

>>> x = "Mississippi"
>>> x.count("ss")
2

>>> x = "Mississippi"
>>> x.startswith("Miss")
True
>>> x.startswith("Mist")
False
>>> x.endswith("pi")
True
>>> x.endswith("p")
False

>>> x.endswith(("i", "u"))
True


6.4.5 Modifying

>>> x = "Mississippi"
>>> x.replace("ss", "+++")
'Mi+++i+++ippi'

>>> x = "~x ^ (y % z)"
>>> table = x.maketrans("~^()", "!&[]")
>>> x.translate(table)
'!x & [y % z]'


6.4.6 Modifying with list manipulations

>>> text = "Hello, World"
>>> wordList = list(text)
>>> wordList[6:] = []
>>> wordList.reverse()
>>> text = "".join(wordList)
>>> print(text)
,olleH

6.4.7 Useful methods and constants

>>> x = "123"
>>> x.isdigit()
True
>>> x.isalpha()
False
>>> x = "M"
>>> x.islower()
False
>>> x.isupper()
True
>>>

6.5 converting objects to strings

>>> repr([1, 2, 3])
'[1, 2, 3]'
>>> x = [1]
>>> x.append(2)
>>> x.append([3, 4])
>>> 'the list x is ' + repr(x)
'the list x is [1, 2, [3, 4]]'

>>> repr(len)
'<built-in function len>'

6.6 formatting with %

>>> "%s is the %s of %s" % ("Ambrosia", "food", "the gods")
'Ambrosia is the food of the gods'

>>> "%s is the %s of %s" % ("Nectar", "drink", "gods")
'Nectar is the drink of gods'
>>> "%s is the %s of the %s" % ("Brussels Sprouts", "food", 
...        "foolish")
'Brussels Sprouts is the food of the foolish'

>>> x = [1, 2, "three"]
>>> "The %s contains: %s"%("list", x)
"The list contains: [1, 2, 'three']"


6.6.1 formatting sequences

>>> "Pi is <%-6.2f>" % 3.14159 # use of the formatting sequence: %–6.2f
'Pi is <3.14  >'

6.6.2 named parameters

>>> num_dict = { 'e' : 2.718, 'pi' : 3.14159 }
>>> print("%(pi).2f - %(pi).4f - %(e).2f" % num_dict)
3.14 - 3.1416 - 2.72

6.7.1 Format method

>>> "{0} is the {1} of {2}".format("Ambrosia", "food", "the gods")
'Ambrosia is the food of the gods'
>>> "{{Ambrosia}} is the {0} of {1}".format("food", "the gods")
'{Ambrosia} is the food of the gods'

6.7.2 Format method, named params

>>> "{food} is the food of {user}".format(food="Ambrosia", user="the gods") 
'Ambrosia is the food of the gods'

>>> "{0} is the food of {user[1]}".format("Ambrosia", 
...          user = ["men", "the gods", "others"]) 
'Ambrosia is the food of the gods'

6.7.3 Format specifiers

>>> "{0:10} is the food of gods".format("Ambrosia")
'Ambrosia   is the food of gods'
>>> "{0:{1}} is the food of gods".format("Ambrosia", 10)
'Ambrosia   is the food of gods'
>>> "{food:{width}} is the food of gods".format(food="Ambrosia", width=10) 
'Ambrosia   is the food of gods'
>>> "{0:>10} is the food of gods".format("Ambrosia")
'  Ambrosia is the food of gods'
>>> "{0:&>10} is the food of gods".format("Ambrosia")
'&&Ambrosia is the food of gods'

6.8 Bytes

>>> unicode_a_with_acute = '\N{LATIN SMALL LETTER A WITH ACUTE}'
>>> unicode_a_with_acute
'á'
>>> xb = unicode_a_with_acute.encode()
>>> xb
b'\xc3\xa1'
>>> xb += 'A'
Traceback (most recent call last):
  File "<pyshell#35>", line 1, in <module>
    xb += 'A'
TypeError: can't concat bytes to str
>>> xb.decode()
'á'