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1 Lists and Tuples |
1 Lists and Tuples |
2 ================ |
2 ================ |
3 |
3 |
4 Python provides an intuitive way to represent a group items, called *Lists*. The |
4 Python provides an intuitive way to represent a group items, called *Lists*. The |
5 items of a *List* are called its elements. Unlike C/C++, elements can be of any |
5 items of a *List* are called its elements. Unlike C/C++, elements can be of any |
6 type. A *List* is represented as a list of comma-sepated elements with paren- |
6 type. A *List* is represented as a list of comma-sepated elements with square |
7 thesis around them:: |
7 brackets around them:: |
8 |
8 |
9 >>> a = [10, 'Python programming', 20.3523, 23, 3534534L] |
9 >>> a = [10, 'Python programming', 20.3523, 23, 3534534L] |
10 >>> a |
10 >>> a |
11 [10, 'Python programming', 20.3523, 23, 3534534L] |
11 [10, 'Python programming', 20.3523, 23, 3534534L] |
12 |
12 |
349 >>> b |
349 >>> b |
350 [1, 3, 4, 5, 7] |
350 [1, 3, 4, 5, 7] |
351 >>> a |
351 >>> a |
352 [5, 1, 3, 7, 4] |
352 [5, 1, 3, 7, 4] |
353 |
353 |
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354 |
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355 List Comprehensions |
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356 ------------------- |
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357 |
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358 List Comprehension is a convenvience utility provided by Python. It is a |
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359 syntatic sugar to create *Lists*. Using *List Comprehensions* one can create |
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360 *Lists* from other type of sequential data structures or other *Lists* itself. |
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361 The syntax of *List Comprehensions* consists of a square brackets to indicate |
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362 the result is a *List* within which we include at least one **for** clause and |
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363 multiple **if** clauses. It will be more clear with an example:: |
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364 |
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365 >>> num = [1, 2, 3] |
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366 >>> sq = [x*x for x in num] |
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367 >>> sq |
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368 [1, 4, 9] |
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369 >>> all_num = [1, 2, 3, 4, 5, 6, 7, 8, 9] |
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370 >>> even = [x for x in all_num if x%2 == 0] |
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371 |
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372 The syntax used here is very clear from the way it is written. It can be |
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373 translated into english as, "for each element x in the list all_num, |
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374 if remainder of x divided by 2 is 0, add x to the list." |
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375 |