It's pretty simple really:
a[start:end] # items start through end-1
a[start:] # items start through the rest of the array
a[:end] # items from the beginning through end-1
a[:] # a copy of the whole array
There is also the `step` value, which can be used with any of the above:
a[start:end:step] # start through not past end, by step
The key point to remember is that the `:end` value represents the first value that is *not* in the selected slice. So, the difference beween `end` and `start` is the number of elements selected (if `step` is 1, the default).
The other feature is that `start` or `end` may be a *negative* number, which means it counts from the end of the array instead of the beginning. So:
a[-1] # last item in the array
a[-2:] # last two items in the array
a[:-2] # everything except the last two items
Python is kind to the programmer if there are fewer items than you ask for. For example, if you ask for `a[:-2]` and `a` only contains one element, you get an empty list instead of an error. Sometimes you would prefer the error, so you have to be aware that this may happen.
Learn python for fun.The popular blog with questions and answers to the python.Solutions to facebookhackercup,codejam,codechef.The fun way to learn python with me.Building some cool apps.
a[start:end] # items start through end-1
a[start:] # items start through the rest of the array
a[:end] # items from the beginning through end-1
a[:] # a copy of the whole array
There is also the `step` value, which can be used with any of the above:
a[start:end:step] # start through not past end, by step
The key point to remember is that the `:end` value represents the first value that is *not* in the selected slice. So, the difference beween `end` and `start` is the number of elements selected (if `step` is 1, the default).
The other feature is that `start` or `end` may be a *negative* number, which means it counts from the end of the array instead of the beginning. So:
a[-1] # last item in the array
a[-2:] # last two items in the array
a[:-2] # everything except the last two items
Python is kind to the programmer if there are fewer items than you ask for. For example, if you ask for `a[:-2]` and `a` only contains one element, you get an empty list instead of an error. Sometimes you would prefer the error, so you have to be aware that this may happen.
Learn python for fun.The popular blog with questions and answers to the python.Solutions to facebookhackercup,codejam,codechef.The fun way to learn python with me.Building some cool apps.
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