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Slicing Copyright © Software Carpentry 2010 This work is licensed under the Creative Commons Attribution License See http://software-carpentry.org/license.html for more information. Python
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Slicing Lists, strings, and tuples are all sequences
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PythonSlicing Lists, strings, and tuples are all sequences Can be indexed by integers in the range 0…len(X)-1
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PythonSlicing Lists, strings, and tuples are all sequences Can be indexed by integers in the range 0…len(X)-1 Can also be sliced using a range of indices
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PythonSlicing Lists, strings, and tuples are all sequences Can be indexed by integers in the range 0…len(X)-1 Can also be sliced using a range of indices >>> element = 'uranium' >>> uranium 01234567 -7-6-5-4-3-2
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PythonSlicing Lists, strings, and tuples are all sequences Can be indexed by integers in the range 0…len(X)-1 Can also be sliced using a range of indices >>> element = 'uranium' >>> print element[1:4] ran >>> uranium 01234567 -7-6-5-4-3-2
![PythonSlicing Lists, strings, and tuples are all sequences Can be indexed by integers in the range 0…len(X)-1 Can also be sliced using a range of indices >>> element = uranium >>> print element[1:4] ran >>> uranium](http://images.slideplayer.com./12/3487962/slides/slide_6.jpg "PythonSlicing Lists, strings, and tuples are all sequences Can be indexed by integers in the range 0…len(X)-1 Can also be sliced using a range of indices >>> element = uranium >>> print element[1:4] ran >>> uranium")
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PythonSlicing Lists, strings, and tuples are all sequences Can be indexed by integers in the range 0…len(X)-1 Can also be sliced using a range of indices >>> element = 'uranium' >>> print element[1:4] ran >>> print element[:4] uran >>> uranium 01234567 -7-6-5-4-3-2
![PythonSlicing Lists, strings, and tuples are all sequences Can be indexed by integers in the range 0…len(X)-1 Can also be sliced using a range of indices >>> element = uranium >>> print element[1:4] ran >>> print element[:4] uran >>> uranium](http://images.slideplayer.com./12/3487962/slides/slide_7.jpg "PythonSlicing Lists, strings, and tuples are all sequences Can be indexed by integers in the range 0…len(X)-1 Can also be sliced using a range of indices >>> element = uranium >>> print element[1:4] ran >>> print element[:4] uran >>> uranium")
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PythonSlicing Lists, strings, and tuples are all sequences Can be indexed by integers in the range 0…len(X)-1 Can also be sliced using a range of indices >>> element = 'uranium' >>> print element[1:4] ran >>> print element[:4] uran >>> print element[4:] ium >>> uranium 01234567 -7-6-5-4-3-2
![PythonSlicing Lists, strings, and tuples are all sequences Can be indexed by integers in the range 0…len(X)-1 Can also be sliced using a range of indices >>> element = uranium >>> print element[1:4] ran >>> print element[:4] uran >>> print element[4:] ium >>> uranium](http://images.slideplayer.com./12/3487962/slides/slide_8.jpg "PythonSlicing Lists, strings, and tuples are all sequences Can be indexed by integers in the range 0…len(X)-1 Can also be sliced using a range of indices >>> element = uranium >>> print element[1:4] ran >>> print element[:4] uran >>> print element[4:] ium >>> uranium")
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PythonSlicing Lists, strings, and tuples are all sequences Can be indexed by integers in the range 0…len(X)-1 Can also be sliced using a range of indices >>> element = 'uranium' >>> print element[1:4] ran >>> print element[:4] uran >>> print element[4:] ium >>> print element[-4:] nium >>> uranium 01234567 -7-6-5-4-3-2
![PythonSlicing Lists, strings, and tuples are all sequences Can be indexed by integers in the range 0…len(X)-1 Can also be sliced using a range of indices >>> element = uranium >>> print element[1:4] ran >>> print element[:4] uran >>> print element[4:] ium >>> print element[-4:] nium >>> uranium](http://images.slideplayer.com./12/3487962/slides/slide_9.jpg "PythonSlicing Lists, strings, and tuples are all sequences Can be indexed by integers in the range 0…len(X)-1 Can also be sliced using a range of indices >>> element = uranium >>> print element[1:4] ran >>> print element[:4] uran >>> print element[4:] ium >>> print element[-4:] nium >>> uranium")
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PythonSlicing Python checks bounds when indexing
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PythonSlicing Python checks bounds when indexing But truncates when slicing
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PythonSlicing Python checks bounds when indexing But truncates when slicing >>> element = 'uranium' >>> uranium 01234567 -7-6-5-4-3-2
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PythonSlicing Python checks bounds when indexing But truncates when slicing >>> element = 'uranium' >>> print element[400] IndexError: string index out of range >>> uranium 01234567 -7-6-5-4-3-2
![PythonSlicing Python checks bounds when indexing But truncates when slicing >>> element = uranium >>> print element[400] IndexError: string index out of range >>> uranium](http://images.slideplayer.com./12/3487962/slides/slide_13.jpg "PythonSlicing Python checks bounds when indexing But truncates when slicing >>> element = uranium >>> print element[400] IndexError: string index out of range >>> uranium")
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PythonSlicing Python checks bounds when indexing But truncates when slicing >>> element = 'uranium' >>> print element[400] IndexError: string index out of range >>> print element[1:400] ranium >>> uranium 01234567 -7-6-5-4-3-2
![PythonSlicing Python checks bounds when indexing But truncates when slicing >>> element = uranium >>> print element[400] IndexError: string index out of range >>> print element[1:400] ranium >>> uranium](http://images.slideplayer.com./12/3487962/slides/slide_14.jpg "PythonSlicing Python checks bounds when indexing But truncates when slicing >>> element = uranium >>> print element[400] IndexError: string index out of range >>> print element[1:400] ranium >>> uranium")
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PythonSlicing Python checks bounds when indexing But truncates when slicing >>> element = 'uranium' >>> print element[400] IndexError: string index out of range >>> print element[1:400] ranium >>> uranium 01234567 -7-6-5-4-3-2 "A foolish consistency is the hobgoblin of little minds." —Ralph Waldo Emerson
![PythonSlicing Python checks bounds when indexing But truncates when slicing >>> element = uranium >>> print element[400] IndexError: string index out of range >>> print element[1:400] ranium >>> uranium A foolish consistency is the hobgoblin of little minds. —Ralph Waldo Emerson](http://images.slideplayer.com./12/3487962/slides/slide_15.jpg "PythonSlicing Python checks bounds when indexing But truncates when slicing >>> element = uranium >>> print element[400] IndexError: string index out of range >>> print element[1:400] ranium >>> uranium A foolish consistency is the hobgoblin of little minds. —Ralph Waldo Emerson")
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PythonSlicing Python checks bounds when indexing But truncates when slicing >>> element = 'uranium' >>> print element[400] IndexError: string index out of range >>> print element[1:400] ranium >>> uranium 01234567 -7-6-5-4-3-2 "A foolish consistency is the hobgoblin of little minds." —Ralph Waldo Emerson "Aw, you're kidding me!" —programmers
![PythonSlicing Python checks bounds when indexing But truncates when slicing >>> element = uranium >>> print element[400] IndexError: string index out of range >>> print element[1:400] ranium >>> uranium A foolish consistency is the hobgoblin of little minds. —Ralph Waldo Emerson Aw, you re kidding me! —programmers](http://images.slideplayer.com./12/3487962/slides/slide_16.jpg "PythonSlicing Python checks bounds when indexing But truncates when slicing >>> element = uranium >>> print element[400] IndexError: string index out of range >>> print element[1:400] ranium >>> uranium A foolish consistency is the hobgoblin of little minds. —Ralph Waldo Emerson Aw, you re kidding me! —programmers")
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PythonSlicing So text[1:3] is 0, 1, or 2 characters long
![PythonSlicing So text[1:3] is 0, 1, or 2 characters long](http://images.slideplayer.com./12/3487962/slides/slide_17.jpg "PythonSlicing So text[1:3] is 0, 1, or 2 characters long")
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PythonSlicing So text[1:3] is 0, 1, or 2 characters long '' 'a''' 'ab''b' 'abc''bc' 'abcdef''bc'
![PythonSlicing So text[1:3] is 0, 1, or 2 characters long a ab b abc bc abcdef bc](http://images.slideplayer.com./12/3487962/slides/slide_18.jpg "PythonSlicing So text[1:3] is 0, 1, or 2 characters long a ab b abc bc abcdef bc")
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PythonSlicing For consistency, text[1:1] is the empty string
![PythonSlicing For consistency, text[1:1] is the empty string](http://images.slideplayer.com./12/3487962/slides/slide_19.jpg "PythonSlicing For consistency, text[1:1] is the empty string")
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PythonSlicing For consistency, text[1:1] is the empty string –From index 1 up to (but not including) index 1
![PythonSlicing For consistency, text[1:1] is the empty string –From index 1 up to (but not including) index 1](http://images.slideplayer.com./12/3487962/slides/slide_20.jpg "PythonSlicing For consistency, text[1:1] is the empty string –From index 1 up to (but not including) index 1")
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PythonSlicing For consistency, text[1:1] is the empty string –From index 1 up to (but not including) index 1 And text[3:1] is always the empty string
![PythonSlicing For consistency, text[1:1] is the empty string –From index 1 up to (but not including) index 1 And text[3:1] is always the empty string](http://images.slideplayer.com./12/3487962/slides/slide_21.jpg "PythonSlicing For consistency, text[1:1] is the empty string –From index 1 up to (but not including) index 1 And text[3:1] is always the empty string")
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PythonSlicing For consistency, text[1:1] is the empty string –From index 1 up to (but not including) index 1 And text[3:1] is always the empty string –Not the reverse of text[1:3]
![PythonSlicing For consistency, text[1:1] is the empty string –From index 1 up to (but not including) index 1 And text[3:1] is always the empty string –Not the reverse of text[1:3]](http://images.slideplayer.com./12/3487962/slides/slide_22.jpg "PythonSlicing For consistency, text[1:1] is the empty string –From index 1 up to (but not including) index 1 And text[3:1] is always the empty string –Not the reverse of text[1:3]")
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PythonSlicing For consistency, text[1:1] is the empty string –From index 1 up to (but not including) index 1 And text[3:1] is always the empty string –Not the reverse of text[1:3] But text[1:-1] is everything except the first and last characters
![PythonSlicing For consistency, text[1:1] is the empty string –From index 1 up to (but not including) index 1 And text[3:1] is always the empty string –Not the reverse of text[1:3] But text[1:-1] is everything except the first and last characters](http://images.slideplayer.com./12/3487962/slides/slide_23.jpg "PythonSlicing For consistency, text[1:1] is the empty string –From index 1 up to (but not including) index 1 And text[3:1] is always the empty string –Not the reverse of text[1:3] But text[1:-1] is everything except the first and last characters")
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PythonSlicing Slicing always creates a new collection
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PythonSlicing Slicing always creates a new collection Beware of aliasing
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PythonSlicing Slicing always creates a new collection Beware of aliasing >>> points = [[10, 10], [20, 20], [30, 30], [40, 40]] >>>
![PythonSlicing Slicing always creates a new collection Beware of aliasing >>> points = [[10, 10], [20, 20], [30, 30], [40, 40]] >>>](http://images.slideplayer.com./12/3487962/slides/slide_26.jpg "PythonSlicing Slicing always creates a new collection Beware of aliasing >>> points = [[10, 10], [20, 20], [30, 30], [40, 40]] >>>")
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PythonSlicing Slicing always creates a new collection Beware of aliasing >>> points = [[10, 10], [20, 20], [30, 30], [40, 40]] >>> middle = points[1:-1] >>>
![PythonSlicing Slicing always creates a new collection Beware of aliasing >>> points = [[10, 10], [20, 20], [30, 30], [40, 40]] >>> middle = points[1:-1] >>>](http://images.slideplayer.com./12/3487962/slides/slide_27.jpg "PythonSlicing Slicing always creates a new collection Beware of aliasing >>> points = [[10, 10], [20, 20], [30, 30], [40, 40]] >>> middle = points[1:-1] >>>")
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PythonSlicing Slicing always creates a new collection Beware of aliasing >>> points = [[10, 10], [20, 20], [30, 30], [40, 40]] >>> middle = points[1:-1] >>> middle[0][0] = 'whoops' >>>
![PythonSlicing Slicing always creates a new collection Beware of aliasing >>> points = [[10, 10], [20, 20], [30, 30], [40, 40]] >>> middle = points[1:-1] >>> middle[0][0] = whoops >>>](http://images.slideplayer.com./12/3487962/slides/slide_28.jpg "PythonSlicing Slicing always creates a new collection Beware of aliasing >>> points = [[10, 10], [20, 20], [30, 30], [40, 40]] >>> middle = points[1:-1] >>> middle[0][0] = whoops >>>")
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PythonSlicing Slicing always creates a new collection Beware of aliasing >>> points = [[10, 10], [20, 20], [30, 30], [40, 40]] >>> middle = points[1:-1] >>> middle[0][0] = 'whoops' >>> middle[1][0] = 'aliasing' >>>
![PythonSlicing Slicing always creates a new collection Beware of aliasing >>> points = [[10, 10], [20, 20], [30, 30], [40, 40]] >>> middle = points[1:-1] >>> middle[0][0] = whoops >>> middle[1][0] = aliasing >>>](http://images.slideplayer.com./12/3487962/slides/slide_29.jpg "PythonSlicing Slicing always creates a new collection Beware of aliasing >>> points = [[10, 10], [20, 20], [30, 30], [40, 40]] >>> middle = points[1:-1] >>> middle[0][0] = whoops >>> middle[1][0] = aliasing >>>")
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PythonSlicing Slicing always creates a new collection Beware of aliasing >>> points = [[10, 10], [20, 20], [30, 30], [40, 40]] >>> middle = points[1:-1] >>> middle[0][0] = 'whoops' >>> middle[1][0] = 'aliasing' >>> print middle [['whoops', 20], ['aliasing', 30]] >>>
![PythonSlicing Slicing always creates a new collection Beware of aliasing >>> points = [[10, 10], [20, 20], [30, 30], [40, 40]] >>> middle = points[1:-1] >>> middle[0][0] = whoops >>> middle[1][0] = aliasing >>> print middle [[ whoops , 20], [ aliasing , 30]] >>>](http://images.slideplayer.com./12/3487962/slides/slide_30.jpg "PythonSlicing Slicing always creates a new collection Beware of aliasing >>> points = [[10, 10], [20, 20], [30, 30], [40, 40]] >>> middle = points[1:-1] >>> middle[0][0] = whoops >>> middle[1][0] = aliasing >>> print middle [[ whoops , 20], [ aliasing , 30]] >>>")
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PythonSlicing Slicing always creates a new collection Beware of aliasing >>> points = [[10, 10], [20, 20], [30, 30], [40, 40]] >>> middle = points[1:-1] >>> middle[0][0] = 'whoops' >>> middle[1][0] = 'aliasing' >>> print middle [['whoops', 20], ['aliasing', 30]] >>> print points [[10, 10], ['whoops', 20], ['aliasing', 30], [40, 40]] >>>
![PythonSlicing Slicing always creates a new collection Beware of aliasing >>> points = [[10, 10], [20, 20], [30, 30], [40, 40]] >>> middle = points[1:-1] >>> middle[0][0] = whoops >>> middle[1][0] = aliasing >>> print middle [[ whoops , 20], [ aliasing , 30]] >>> print points [[10, 10], [ whoops , 20], [ aliasing , 30], [40, 40]] >>>](http://images.slideplayer.com./12/3487962/slides/slide_31.jpg "PythonSlicing Slicing always creates a new collection Beware of aliasing >>> points = [[10, 10], [20, 20], [30, 30], [40, 40]] >>> middle = points[1:-1] >>> middle[0][0] = whoops >>> middle[1][0] = aliasing >>> print middle [[ whoops , 20], [ aliasing , 30]] >>> print points [[10, 10], [ whoops , 20], [ aliasing , 30], [40, 40]] >>>")
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PythonSlicing 10 20 30 40 points
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PythonSlicing 10 20 30 40 points middle
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PythonSlicing 10 20 30 40 points middle 'whoops'
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PythonSlicing 10 20 30 40 points middle 'whoops' 'aliasing'
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October 2010 created by Greg Wilson Copyright © Software Carpentry 2010 This work is licensed under the Creative Commons Attribution License See http://software-carpentry.org/license.html for more information.
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