The list type implements the sequence protocol, and also allows you to add and remove objects from the sequence.
Various ways to iterate over sequences The sequence functions illustrated in 4. We can randomize the contents of a list s before iterating over them, using random. We can convert between these sequence types.
For example, tuple s converts any kind of sequence into a tuple, and list s converts any kind of sequence into a list. We can convert a list of strings to a single string using the join function, e.
Some other objects, such as a FreqDist, can be converted into a sequence using list or sorted and support iteration, e. We can omit the parentheses because the comma has higher precedence than assignment.
It is equivalent to the following traditional way of doing such tasks that does not use tuples notice that this method needs a temporary variable tmp. There are also functions that modify the structure of a sequence and which can be handy for language processing.
Thus, zip takes the items of two or more sequences and "zips" them together into a single list of tuples. Given a sequence s, enumerate s returns pairs consisting of an index and the item at that index.
For some NLP tasks it is necessary to cut up a sequence into two or more parts. To do this we decide the location where we want to cut the datathen cut the sequence at that location.
We can also verify that the ratio of the sizes of the two pieces is what we intended. Combining Different Sequence Types Let's combine our knowledge of these three sequence types, together with list comprehensions, to perform the task of sorting the words in a string by their length.
A simple string is actually an object with methods defined on it such as split. We use a list comprehension to build a list of tupleswhere each tuple consists of a number the word length and the word, e. We use the sort method to sort the list in-place.
Finally, we discard the length information and join the words back into a single string. The underscore is just a regular Python variable, but we can use underscore by convention to indicate that we will not use its value.
We began by talking about the commonalities in these sequence types, but the above code illustrates important differences in their roles. First, strings appear at the beginning and the end: Lists and tuples are used in the middle, but for different purposes.
A list is typically a sequence of objects all having the same type, of arbitrary length. We often use lists to hold sequences of words. In contrast, a tuple is typically a collection of objects of different types, of fixed length.
We often use a tuple to hold a record, a collection of different fields relating to some entity. This distinction between the use of lists and tuples takes some getting used to, so here is another example: An individual entry is represented as a tuple because it is a collection of objects with different interpretations, such as the orthographic form, the part of speech, and the pronunciations represented in the SAMPA computer-readable phonetic alphabet http: Note that these pronunciations are stored using a list.
Note A good way to decide when to use tuples vs lists is to ask whether the interpretation of an item depends on its position. For example, a tagged token combines two strings having different interpretation, and we choose to interpret the first item as the token and the second item as the tag.
Thus we use tuples like this: In contrast, the elements of a text are all tokens, and position is not significant. Thus we use lists like this: The linguistic meaning of the words might be different, but the interpretation of list items as tokens is unchanged.
The distinction between lists and tuples has been described in terms of usage. However, there is a more fundamental difference: In other words, lists can be modified, while tuples cannot. Here are some of the operations on lists that do in-place modification of the list. Generator Expressions We've been making heavy use of list comprehensions, for compact and readable processing of texts.
Here's an example where we tokenize and normalize a text:An assignment statement evaluates the expression list (remember that this can be a single expression or a comma-separated list, the latter yielding a tuple) and assigns the single resulting object to each of the target lists, from left to right.
Assignment is defined recursively depending on the. Python Basic Operators - Learn Python in simple and easy steps starting from basic to advanced concepts with examples including Python Syntax Object Oriented Language, Methods, Tuples, Tools/Utilities, Exceptions Handling, Sockets, GUI, Extentions, XML Programming.
Licenses. All Python releases are Open iridis-photo-restoration.comically, most, but not all, Python releases have also been GPL-compatible. The Licenses page details GPL-compatibility and Terms and Conditions. Python Assignment Operators Example - Learn Python in simple and easy steps starting from basic to advanced concepts with examples including Python Syntax Object Oriented Language, Methods, Tuples, Tools/Utilities, Exceptions Handling, Sockets, GUI, Extentions, XML Programming.
The Python language has distinct concepts for expressions and statements. Assignment is a statement even if the syntax sometimes tricks you into thinking it's an expression (e.g. a=b=99 works but is a special syntax case and doesn't mean that the b=99 is an expression like it is for example in C).
List comprehensions are instead expressions because they return a value, in a sense the loop they. Licenses. All Python releases are Open iridis-photo-restoration.comically, most, but not all, Python releases have also been GPL-compatible.
The Licenses page details GPL-compatibility and Terms and Conditions.