Strings in Python
In Python, strings are sequences of characters enclosed in single, double, or triple quotes. They can be manipulated using various built-in string methods and operators. Strings are immutable, meaning they cannot be changed after they are created, and they are widely used for representing text data in Python programs.
4 Key excerpts on "Strings in Python"
- Yasha Hasija, Rajkumar Chakraborty(Authors)
- 2021(Publication Date)
- CRC Press(Publisher)
...Please note that we have a dedicated section for classes and functions in this chapter, so just remember this part for now. Strings For computer programmers, strings are the collection of characters or, more commonly, any texts. In bioinformatics studies, handling strings is very common - like sequencing files, finding patterns in the sequences, data-mining from texts, processing data from various file formats, etc. By enclosing a sequence of characters between a pair of single quotes, double quotes, triple-single quotes, or triple-double quotes, a string object can be constructed in Python. While characters enclosed between single or double quotes can only have a single line, characters between triple-single or triple-double quotes can have multiple lines. Let us take a look at the following example: Code: # A string within a pair of single quotes seq_1 = 'ATGCGTCA' print(seq_1) print('---------') # A string within a pair of double quotes seq_2 = "ATGCGTCA" print(seq_2) print('---------') # A string within a pair of triple single quotes seq_3 = '''ATGCGTCA''' print(seq_3) print('---------') # A string within a pair of triple double quotes seq_4 = """ATGCGTCA""" print(seq_4) print('---------') # A string within a pair of triple single quotes, can have multiple lines seq_5 = '''MALNSGSPPA IGPYYENHGY''' print(seq_5) print('---------') # A string within a pair of triple double quotes, can have multiple lines seq_6 = """IGPYYENHGY IGPYYENHGY""" print(seq_6) Output: ATGCGTCA --------- ATGCGTCA --------- ATGCGTCA --------- ATGCGTCA --------- IGPYYENHGY --------- IGPYYENHGY IGPYYENHGY The characters should be enclosed within the same type of quote - usually single or double quotes - for defining a string datatype. Escape Sequence Characters Supposing the user. has to print text in different lines using double or single quotes, as programmers generally like to use double or single quotes for defining text. Perhaps, the user wants to use quotes inside quotes or more...
eBook - ePubData Science and Machine Learning
Mathematical and Statistical Methods
- Dirk P. Kroese, Zdravko Botev, Thomas Taimre, Radislav Vaisman(Authors)
- 2019(Publication Date)
- Chapman and Hall/CRC(Publisher)
...Strings are immutable as well. x = (1,2) x[0] = 2 TypeError: 'tuple ' object does not support item assignment I MMUTABLE Lists can be accessed via the slice notation [ start:end ]. It is important to note that end is the index of the first element that will not be selected, and that the first element has index 0. To gain familiarity with the slice notation, execute each of the following lines. a = [2, 3, 5, 7, 11, 13, 17, 19, 23] a[1:4] # Elements with index from 1 to 3 a[:4] # All elements with index less than 4 a[3:] # All elements with index 3 or more a[−2:] # The last two elements [3, 5, 7] [2, 3, 5, 7] [7, 11, 13, 17, 19, 23] [19, 23] S LICE An operator is a programming language construct that performs an action on one or more operands. The action of an operator in Python depends on the type of the operand(s). For example, operators such as +, *, −, and % that are arithmetic operators when the operands are of a numeric type, can have different meanings for objects of non-numeric type (such as strings). 'hello' + 'world' # String concatenation 'helloworld ' 'hello' * 2 # String repetition 'hellohello ' [1,2] * 2 # List repetition [1, 2, 1, 2] 15 % 4 # Remainder of 15/4 3 O PERATOR Some common Python operators are given in Table D.1. ☞ 469 D.2 Python Objects As mentioned in the previous section, data in Python is represented by objects or relations between objects. We recall that basic data types included strings and numeric types (such as integers, booleans, and floats). As Python is an object-oriented programming language, functions are objects too (everything is an object!). Each object has an identity (unique to each object and immutable — that is, cannot be changed — once created), a type (which determines which operations can be applied to the object, and is considered immutable), and a value (which is either mutable or immutable)...
eBook - ePubBioinformatics Algorithms
Design and Implementation in Python
- Miguel Rocha, Pedro G. Ferreira(Authors)
- 2018(Publication Date)
- Academic Press(Publisher)
...Strings, lists, and tuples are sequence types since they have an implicit order of their elements, which can be accessed by an index value. Sets and dictionaries represent a collection of unordered elements. The set type implements the mathematical concept of sets of elements (any object), where the position or order of the elements is not maintained. Dictionaries are a mapping type, since they rely on a hashing strategy to map keys to the corresponding values, which can be any object. One important characteristic of some of these data types is that once the variables are created their value cannot be changed. These are called immutable types and include strings, tuples, and sets. An attempt to alter the composition of a variable of one of these types generates an error. Table 2.1 provides a summary of the different features of Python primitive and container data types. The last column indicates if the container type allows different types of their elements or not. Table 2.1 Features of Python built-in data types. Data type Complexity Order Mutable Indexed Heterogeneous int primitive – yes – – float primitive – yes – – complex primitive – yes – – Boolean primitive – yes – – string container yes no yes no list container yes yes yes yes tuple container yes no yes yes set container no no no yes dictionary container no yes no yes In Python, the data type is not defined explicitly and it is assumed during the execution by taking into. account the computation context and the values assigned to the variable. This results in a more compact and clear code syntax, but may raise execution errors, for instance when the name of a variable is incorrectly written or when non-operations are performed (e.g. sum of an integer with a string). 2.2.2 Assigning Values to Variables In Python, the operator = is used to assign a value to a variable name. It is the core operation in any computer program, that allows to define the dynamics of the code...
eBook - ePub- Joy Ko, Kyle Steinfeld(Authors)
- 2018(Publication Date)
- Routledge(Publisher)
...Despite this property which is typically associated with structured data types, Strings are paradoxically immutable and thus behave more like primitive types within the Python object model. While a String that contains just one character is still a String in Python, in many other languages, Strings are comprised of a more elemental type called a Char. Strings will be discussed in detail in Chapter 1.04. Structured Data Types In contrast with primitive types, structured data types are organized composites of lower-level data. These lower-level composites might be primitive types, or may themselves be structured of lower levels still. Where primitive types may be elucidated by a discussion of their basic interactions via operators, the behavior of structured types varies widely depending on their composition. The salient quality of structured data types arises from the fact that they are composed of other objects in the object model. This brings to the foreground a number of complications regarding the nature of these composite objects, and of the object model itself, that must be grasped in order for them to be applied and authored effectively. Structured data types that we will encounter in this text include all collection types, such as Lists and Dictionaries, as well as any class imported from a module, such as the Point, Vec, and Line classes found in the Decod.es library. Two concerns that arise from the nature of structured types are examined here. The first relates to the design of data types, and the second extends an earlier discussion of how variables bind with structured objects in Python. The Structure of Structured Data Types As we shall see in Chapter 1.11, the design of classes is as much art as science, and there exist many possible paths to achieve similar results...
