Programming in Python. Working with strings

In the daily life of the programmer need to solve a lot of problems. For these purposes, perfect Python language (“online” or “Python” on Russian manners). Backup, creating games for Android or for Windows, read and save messages from e-mail – not the most difficult task for an experienced programmer. But for beginners to learn Python (work with strings, lists, files,) will seem like a fairy tale, because the methods and functions of each type of data make life easier for the user.

What is string data type?

“Python” allows you to work with numbers, symbols, files, functions. And difficulties never occurs because this language is convenient and easy to use. Strings in Python – the type of data to process textual information. Length the entered text can be limited only by the computer resources. You need to remember that line – immutable data type. Everything that happens with the original text is assigned to a new variable.

In Python training involves the study of 2 kinds of text: ordinary strings (sequence of bytes) and Unicode string (list of characters).

In Python scripts allow you to use string literals. These symbols can be written using the apostrophe, quotation marks (single or double), the specified characters is entered three times, for example, """apple tree""" where performs the role of the Enter key when typing in a regular text editor. The backslash (back slash) inside of the literals is of special significance. It is necessary to enter special characters. Remember that the backslash must not be last character in the string, otherwise the compiler will issue an error.

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How to create a string?

In Python, working with strings involves either manual entry of the text or prompt to the user that he entered the necessary characters. Python reads the received data using the standard input function (). String in Python consists of a sequence of characters. To know their number, you can use len (). In Python, the symbol is treated as a string, the length of which is equal to 1.

Any object in the “Python” can be cast to string data type by calling a built-in function str (). Python has several classes. To translate an object from one data type to another, you can use the cast function whose name matches the name of the category. So, int converts to an integer, str the string float in the float category.

Sections in the rows

Otherwise, they are referred to as slices or slices. Slice allows you to extract from the typed character in a specified period. Slice cannot be used without indexing. Addressing starts with 0. If you refer to the line from the end, then the indexing begins with -.

There are 3 forms of cuts:

• Extract a single character from whole string St[i], where St – the text i – cell number.
• Get text, St[a:b], where St – the text, a and b – the beginning and end of period. A is included in the slice, the parameter b is not. If in the interval you do not specify b, and put a colon, then the program will return an excerpt, taken to end of line. If you do not set the parameter a, the slice originates from a 0 index to the end of paragraph b.
• Cut St[a:b:d] allows you to select a specific passage in the interval beginning at a and ending at b with step d.

Operations with strings

The user has the ability to use Python functions to work with strings:

• Str(X) – translation of any object in a string data type.
• ST1+ST2 – concatenation (addition of strings).
• ST*n-ST repeat string n times.
• Min [ST] – returns minimum value from a code table.
• Len () – determining the length of the text.
• Max [ST] – obtaining maximum values from the ASCII table.
• St1 in St2 – occurrence of a substring St1 to St2. Returns True if St1 is present in the original text.
• Not in St1, St2 – checks that the St1 to St2 and returns True when the correctness of the statements.

Methods of string data type

In Python, working with strings involves the use of several methods:

• St. find and St.rfind – the methods necessary to search for a passage in the entered text. The difference is that this process will start from different ends. So, St.find searches from the beginning, and St.rfind from the end. The methods return the index of the first occurrence of the searched text. You can specify the sections to search in a particular period.
• St. replace (a_old,b_new) needed to replace all occurrences of the substrings in the entered text. Instead a_old will be b_new. If you specify an additional count parameter (St.replace (a_old,b_new, count)), then the change will occur the number of times is not greater than count.
• St. count – the method required for counting the number of occurrences of substring S in the input text. The number of intersections is not included in the final result. You can specify the length, which will be the operation.
• St. join for concatenating the list of words in a string.
• St. split – a method to turn the string into a list of words. In brackets in quotes to specify the delimiter. Most often it is the space St. split(“ ”).
• St. strip – remove spaces at the beginning and end of the string.
• St. capitalize makes the first character in the text uppercase.
• St. swapcase allows you to convert the case of letters in the opposite direction.
• St. upper gives the opportunity to change all letters to uppercase in the string.
• St. lower allows you to transfer the entered text to lower case. All letters will be lowercase.

Formatted string

In Python, working with strings is nice and the fact that the user can format the text in the specified image. I.e. the programmer specifies the condition which needs to match the entered text. This way you can display the table without connecting a special module PTable. This technique is called a format string. For example, if you enter in IDLE Print "%s is %d" % ("one",1), then the result will be 1 is one.

the% allows you to connect the format string and is its main operator. In Python characters are coming as addition to %.

There are other special characters, but they are used in solving complex tasks.

Multiple problems with solutions

A language like Python allows learning to be faster and easier because the code is concise and comprehensive. To verify this, you need to address a number of problems.

1. Given a string. Get a new text, which replaces all occurrences of the first symbol of the “$” except for himself.

Algorithm:

• Write a function, which:
• A char variable is assigned the first character string;
• Length specifies the length of the string;
• Str1 using the replace method replaces the char with the symbol "$";
• Str1 writes the first character and the resulting expressions from the previous operation;
• Return the value of str1.
• Display the result of the calculation function.

2. Dana...