Adding elements to string python

8 ways to add an element to the beginning of a list and string in Python

Let’s look at different methods for adding elements to the beginning of a list and string: concatenation, insert, append, extend, rjust, and f-strings.

How to add an item to the top of a Python list: 4 methods

Lists in Python are mutable and ordered data structures designed to store a group of values. If you need to insert an element in the first position of an existing list during the program execution, you can use one of the methods described below.

Method 1: insert

This method is implemented using the built-in insert() method of lists. This method works with any type of data and allows you to insert the desired element at any position in the existing list, including the first one. The insert() method takes two parameters – the index (position) at which the element is to be inserted, and the element itself. Counting positions in Python starts from zero – Accordingly, to insert an element at the beginning of the list , you need to specify 0 , and not, as the first parameter 1 . Let’s take an example. Suppose we have a list [1, 2, 3] where we want to insert the number 5 at the beginning. Use the insert() method:

arr = [1, 2, 3] arr.insert(0, 5) print(arr) 

Источник

How to add characters to an empty string in Python

In this Python tutorial, we will see how to add characters to an empty string in Python with various methods using demonstrative examples.

In Python, a string is a sequence of characters enclosed in either single quotes (‘ ‘) or double quotes (” “). We can assign a string to a variable like this:

We can create an empty string by assigning no characters between the quotes, like this:

Add characters to an empty string in Python

Adding characters to an empty string in Python can be accomplished using many methods. They are:

• + or += Operator
• join() Method
• format() Method
• f-strings
• str() Function
• % Operator

Let’s see them one by one using illustrative examples.

Method-1: Add characters to an empty string in Python using + or += Operator

The most common method of adding characters to an empty string in Python is by using the + or += operator. This operator combines two strings into one.

Consider we’re visiting the Grand Canyon in Arizona. We want to create a string that says, “Visiting the Grand Canyon in Arizona”. We have an empty string called Sentence and we have to add these character that only says “Visiting the”, ” Grand Canyon” and “in Arizona” to it.

Let’s try to add these characters using Python + operator first.

Sentence = "" Sentence = Sentence + 'Visiting the' + ' ' + 'Grand Canyon' + ' ' + 'in Arizona' print(Sentence)

The Output is:

• An empty string is created and assigned to the variable Sentence.
• The Python + operator concatenates the empty string with the characters, and the result is reassigned to Sentence.
• ThePython print() function is then used to output the value of Sentence, which is now:

Visiting the Grand Canyon in Arizona

Note: As we can see the variable(Sentence) is coming twice in one of the line in our code. Being a Python programmer, we should avoid code repetition in our program. So, we can use += operator in the above example to avoid repetition.

In the above example, we can change:

 Sentence = "" Sentence += 'Visiting the' + ' ' + 'Grand Canyon' + ' ' + 'in Arizona' print(Sentence)

The Output: Same as the first one

Visiting the Grand Canyon in Arizona

This way, we can use the + or += operator to add the characters to an empty string in Python.

Method-2: Append characters to an empty string in Python using the join() method

Another approach to append characters or elements to a string in Python is by using the join() method. This method combines a list of strings into a single string with a specified delimiter.

Let’s use the names of the five largest states by population in the USA as an example.

all_states = '' states = ['California', 'Texas', 'Florida', 'New York', 'Pennsylvania'] all_states += ', '.join(states) print(all_states)

The Output is: In the above example, we start with a string in Python, a list of state names, then use the join() method to append to the empty string, with each state name separated by a comma and a space.

California, Texas, Florida, New York, Pennsylvania

This way, we can use the join() method to append characters to an empty string in Python.

Method-3: Add elements to the string in Python using format() method

Python’s format() method can also be used to add characters to an empty string. The method allows us to interpolate specified values into a Python string, which can be particularly useful when constructing complex sentences or messages.

Here’s an example using some of the tallest buildings in the USA:

message = '' building1 = 'One World Trade Center' building2 = 'Central Park Tower' building3 = 'Willis Tower' message += 'The tallest buildings in the USA include <>, <>, and <>.'.format(building1, building2, building3) print(message)

The output is:

The tallest buildings in the USA include One World Trade Center, Central Park Tower, and Willis Tower.

This way, we can use the format() method to add elements to the string in Python.

Method-4: Append characters to empty string in Python using f-strings

Since Python 3.6, we have f-strings, a new way to format strings in Python. They are easy to use and read, making them a great string formatting tool. This can be used to append characters to an empty string in Python.

Let’s use the names of some famous American inventors as an example:

message = '' inventor1 = 'Thomas Edison' inventor2 = 'Alexander Graham Bell' inventor3 = 'Nikola Tesla' message += f'Famous American inventors include , , and .' print(message)

The Output is:

Famous American inventors include Thomas Edison, Alexander Graham Bell, and Nikola Tesla.

This way, we can append characters to empty string in Python using f-strings.

Method-5: Append a letter to a string in python using the str() function

In Python, the str() is a built-in function that converts non-string data types to a string.

Let’s consider the numbers of some major U.S. highways: In this example, the Python str() function is used to convert integer values to strings before concatenating them to other strings.

highway1 = 66 highway2 = 101 highway3 = 61 message = "Major U.S. highways include " + str(highway1) + ", " + str(highway2) + ", and " + str(highway3) + "." print(message)

The output is:

Major U.S. highways include 66, 101, and 61.

This way we can use the str() function to append a letter to a string in Python.

Method-6: Add value to empty string in Python using the % operator

Python also supports C-style string formatting, where substitutions are made using the % operator and a format specifier. Here, we are working on the Python string. So, we need %s as a format specifier.

Let’s try to put the city, state, and, its population in one empty string.

message = '' city = "San Francisco" state = "California" population = 883305 message += "The city of %s is in the state of %s and it has a population of %d." % (city, state, population) print(message)

The output is:

The city of San Francisco is in the state of California and it has a population of 883305.

This way, we can use the % operator to add value to an empty string in Python.

Append character to a string python

Now, we will see how to append a character to a string in Python.

• To append a character to a string, we will insert the character at an index of a string, and it will create a new string with that character.
• To insert a character, we will use slicing a_str[:1] + “n” + a_str[1:], and the “+” operator is used to insert the desired character.

a_str = "Hello" a_str = a_str[:1] + "n" + a_str[1:] print(a_str)

You can refer to the below screenshot to see the output for append character to a string Python

This is how to append a character to a string in Python.

Add a letter to a string Python

Here, we will see how to add a letter to a string Python.

To add a letter to a string python we will use f””, and to get the output, we will print(res).

str1 = "Python" l2 = "G" res = f"" print(res)

You can refer to the below screenshot to see the output for adding a letter to a string Python.

This is Python code to add a letter to a string in Python.

How to append to an empty string in Python

Let’s see how to append to an empty string in Python.

To append to an empty string in Python, we have to use the “+” operator to append in an empty string.

str = "" res = str + "Hello World" print(res)

You can refer to the screenshot below to see the output for appending to an empty Python string.

The above code we can use to append to an empty string in Python.

Conclusion

Adding characters to an empty string in Python is straightforward. Whether you’re concatenating strings using the “+” or “+=” operators or “%” operator or combining a list of strings with the join() method, format() method, using f-string, str() function. Python offers flexible options to suit our needs.

I am Bijay Kumar, a Microsoft MVP in SharePoint. Apart from SharePoint, I started working on Python, Machine learning, and artificial intelligence for the last 5 years. During this time I got expertise in various Python libraries also like Tkinter, Pandas, NumPy, Turtle, Django, Matplotlib, Tensorflow, Scipy, Scikit-Learn, etc… for various clients in the United States, Canada, the United Kingdom, Australia, New Zealand, etc. Check out my profile.

Источник

Добавление символа в строку в Python: лучшие способы и примеры

Вставка символов в строку – это часто встречающаяся задача при работе с текстом на Python. В этой статье мы рассмотрим различные методы вставки символов в строку и предоставим примеры кода для каждого из них.

1. Конкатенация строк

Конкатенация – это простой и интуитивно понятный способ добавления символа или строки к существующей строке. Мы можем использовать оператор + для соединения двух строк вместе.

s = "Hello, World!" char_to_insert = "X" position = 7 new_s = s[:position] + char_to_insert + s[position:] print(new_s) # Вывод: "Hello, XWorld!"

В этом примере мы добавляем символ «X» на позицию 7 в строку «Hello, World!».

2. Использование списков

Так как строки в Python являются неизменяемыми объектами, использование списков может быть более эффективным, особенно при множественных операциях вставки. Мы можем преобразовать строку в список, вставить символ и затем преобразовать список обратно в строку с помощью метода join() .

s = "Hello, World!" char_to_insert = "X" position = 7 s_list = list(s) s_list.insert(position, char_to_insert) new_s = ''.join(s_list) print(new_s) # Вывод: "Hello, XWorld!"

3. Использование строковых методов

Метод str.format() позволяет вставить значения в определенные позиции строки, используя фигурные скобки <> в качестве заполнителей.

s = "Hello, World!" char_to_insert = "X" position = 7 new_s = '<><><>'.format(s[:position], char_to_insert, s[position:]) print(new_s) # Вывод: "Hello, XWorld!"

Мы также можем использовать f-строки, доступные начиная с Python 3.6, для более удобной записи.

s = "Hello, World!" char_to_insert = "X" position = 7 new_s = f'' print(new_s) # Вывод: "Hello, XWorld!"

4. Использование стека

Стек – это структура данных, основанная на принципе «последний вошел, первый вышел» (LIFO). Мы можем использовать стек для хранения символов строки, вставить символ на нужную позицию и затем извлечь символы в новую строку.

def insert_char(s, char_to_insert, position): stack = list(s) new_s = "" for i in range(len(stack) + 1): if i == position: new_s += char_to_insert else: new_s += stack.pop(0) return new_s s = "Hello, World!" char_to_insert = "X" position = 7 new_s = insert_char(s, char_to_insert, position) print(new_s) # Вывод: "Hello, XWorld!"

6. Использование метода str.replace()

Метод str.replace() заменяет все вхождения подстроки на другую подстроку. Мы можем использовать этот метод для вставки символа, заменяя определенный символ или подстроку на исходную подстроку плюс символ для вставки.

s = "Hello, World!" char_to_insert = "X" position = 7 char_to_replace = s[position] new_s = s.replace(char_to_replace, char_to_insert + char_to_replace, 1) print(new_s) # Вывод: "Hello, XWorld!"

Заключение

Каждый из представленных методов имеет свои преимущества и недостатки. Конкатенация строк является простым и интуитивным способом, но может быть неэффективным для больших строк или множественных операций вставки. Использование списков и стеков предлагает более гибкий подход, но может быть менее эффективным для небольших операций. Строковые методы, такие как str.format() и f-строки, предоставляют удобную запись, но могут быть сложными для понимания для новичков.

Источник