Python has powerful built-in support for working with strings. In this post, we'll explore some of the most commonly used string operations, including creating strings, concatenating and repeating strings, changing the case of strings, replacing characters, splitting strings, checking for the existence of words, and formatting strings, all while applying an astronomy theme.
Creating Strings
In Python, you can create strings using single, double, or triple quotes. Here's an example of creating a one-line string and a multi-line string representing the name and description of a planet:
# One-line string planet_name = "Mars" print(f"Planet name: {planet_name}") # Output: Planet name: Mars # Multi-line string planet_description = """Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, being larger than only Mercury. Named after the Roman god of war, it is often referred to as the "Red Planet" because the iron oxide prevalent on its surface gives it a reddish appearance.""" print(f"Planet description: {planet_description}") Output: Planet description: Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, being larger than only Mercury. Named after the Roman god of war, it is often referred to as the "Red Planet" because the iron oxide prevalent on its surface gives it a reddish appearance. Concatenating and Repeating Strings
You can concatenate strings using the + operator, and repeat strings using the * operator. Here's an example of concatenating and repeating strings to create a sentence about the number of moons of a planet:
# Concatenating strings planet_name = "Mars" num_moons = 2 sentence = planet_name + " has " + str(num_moons) + " moons." print(sentence) # Output: Mars has 2 moons. # Repeating strings separator = "-" print(separator * 10) # Output: ---------- Changing the Case of Strings
You can change the case of a string using the upper, lower, capitalize, and title methods. Here's an example of changing the case of a string representing the name of a planet:
# Convert to uppercase planet_name = "Mars" print(planet_name.upper()) # Output: MARS # Convert to lowercase print(planet_name.lower()) # Output: mars # Convert to capitalization print(planet_name.capitalize()) # Output: Mars # Convert to title case print(planet_name.title()) # Output: Mars Replacing Characters
You can replace characters in a string using the replace method. Here's an example of replacing characters in a string representing the name of a planet:
# Replace characters planet_name = "Mars" new_planet_name = planet_name.replace("M", "C") print(new_planet_name) # Output: Cars Splitting and Slicing Strings
You can split the contents of a string using the split method. By default, split splits a string on whitespace, but you can also specify a different separator. Here's an example of splitting a string representing the names of planets, and extracting the domain from an email address:
# Split the contents of a string planets = "Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune" planet_list = planets.split() print(planet_list) # Output: ['Mercury', 'Venus', 'Earth', 'Mars', 'Jupiter', 'Saturn', 'Uranus', 'Neptune'] # Split using a different separator planets = "Mercury,Venus,Earth,Mars,Jupiter,Saturn,Uranus,Neptune" planet_list = planets.split(sep=",") print(planet_list) # Output: ['Mercury', 'Venus', 'Earth', 'Mars', 'Jupiter', 'Saturn', 'Uranus', 'Neptune'] # Extract the domain from an email address email = "astronomer@example.com" domain = email.split(sep="@") print(domain[1]) # Output: example.com Strings can be sliced using the slice() function or using square brackets. The syntax for slicing isstring[start:stop:step], where start is the starting index, stop is the ending index (exclusive), and step is the step size. If start is omitted, slicing starts from the beginning of the string. If stop is omitted, slicing goes to the end of the string. If step is omitted, the step size is 1:
planet = 'Mars' print(planet[1:]) # Output: ars print(planet[2:3]) # Output: r print(planet[:-1]) # Output: Mar sliced = slice(1, 3) print(planet[sliced]) # Output: ar Checking for the Existence of Words
You can check for the existence of a word in a string using the in keyword. Here's an example of checking for the existence of a word in a string representing a sentence about a planet:
# Check for the existence of a word sentence = "Mars is the fourth planet from the Sun." word = "Mars" if word in sentence: print(f"{word} is in the sentence.") else: print(f"{word} is not in the sentence.") # Output: Mars is in the sentence. print("Mars" in "Mars is the fourth planet from the Sun.") # Output: True Obtaining the Number of Occurrences of a Word
You can obtain the number of occurrences of a word in a string using the count method. Here's an example of obtaining the number of occurrences of a word in a string representing a sentence about a planet:
# Obtain the number of occurrences of a word sentence = "Mars is the fourth planet from the Sun. Mars has two moons." word = "Mars" count = sentence.count(word) print(f"{word} occurs {count} times in the sentence.") # Output: Mars occurs 2 times in the sentence. Formatting Strings
You can format strings using the format method or string interpolation (f-strings). Here's an example of formatting a string using the format method and string interpolation, with one or more inputs:
# Format a string using the format method planet_name = "Mars" num_moons = 2 sentence = "{} has {} moons.".format(planet_name, num_moons) print(sentence) # Output: Mars has 2 moons. # Format a string using string interpolation planet_name = "Mars" num_moons = 2 sentence = f"{planet_name} has {num_moons} moons." print(sentence) # Output: Mars has 2 moons. # Format a string with multiple inputs planet1_name = "Earth" planet2_name = "Mars" sentence = f"{planet1_name} and {planet2_name} are neighbouring planets." print(sentence) # Output: Earth and Mars are neighbouring planets. Removing Prefixes and Suffixes
You can remove prefixes and suffixes from a string using the removeprefix and removesuffix methods. Here's an example of removing a prefix and a suffix from a string representing the name of a planet:
# Remove a prefix planet_name = "Planet Mars" new_planet_name = planet_name.removeprefix("Planet ") print(new_planet_name) # Output: Mars # Remove a suffix planet_name = "Mars Planet" new_planet_name = planet_name.removesuffix(" Planet") print(new_planet_name) # Output: Mars Checking if a String Starts with a Certain Word
You can check if a string starts with a certain word or words using the startswith method. Here's an example of checking if a string representing a sentence about a planet starts with a certain word:
# Check if a string starts with a certain word sentence = "Mars is the fourth planet from the Sun." word = "Mars" if sentence.startswith(word): print(f"The sentence starts with {word}.") else: print(f"The sentence does not start with {word}.") # Output: The sentence starts with Mars. Stripping Strings
You can strip whitespace or other characters from the beginning and end of a string using the strip, lstrip, and rstrip methods. Here's an example of stripping whitespace from a string representing the name of a planet:
# Strip whitespace from the beginning and end of a string planet_name = " Mars " stripped_planet_name = planet_name.strip() print(stripped_planet_name) # Output: Mars # Strip whitespace from the beginning of a string planet_name = " Mars " stripped_planet_name = planet_name.lstrip() print(stripped_planet_name) # Output: Mars # Strip whitespace from the end of a string planet_name = " Mars " stripped_planet_name = planet_name.rstrip() print(stripped_planet_name) # Output: Mars Using f-strings
You can use f-strings to format strings in a concise and readable way. Here's an example of using f-strings to format strings representing various astronomical quantities:
import datetime # Format a string using f-strings w = 0.1 x = 2 n = 1234567890 now = datetime.datetime.now() # Display the value of an expression print(f"{w = }") # Output: w = 0.1 print(f"{x % 2 = }") # Output: x % 2 = 0 # Format a number with underscores as a thousand separator print(f"{n:_}") # Output: 1_234_567_890 # Align values print(f"{w:>20}") # Output: 0.1 print(f"{w:<20}") # Output: 0.1 print(f"{w:^20}") # Output: 0.1 # Fill and align values print(f"{w:_>20}") # Output: _________________0.1 print(f"{w:_<20}") # Output: 0.1_________________ print(f"{w:_^20}|") # Output: ________0.1_________| # Format dates print(f"{now = :%Y-%m-%d}") # Output: now = 2024-02-18 print(f"{now = :%c}") # Output: now = Sun Feb 18 00:32:09 2024 print(f"{now = :%I%p}") # Output: now = 12AM Converting Strings
You can convert strings to other types using various functions, including ascii, repr, and str. Here's an example of converting a string representing the name of a planet to ASCII, using the repr function to display the string representation of an object, and converting a number to a string:
# Convert a string to ASCII planet_name = "Mars" ascii_planet_name = ascii(planet_name) print(ascii_planet_name) # Output: 'Mars' # Display the string representation of an object w = "Mars" print(f"{w!r}") # Output: 'Mars' # Convert a number to a string num_moons = 2 str_num_moons = str(num_moons) print(str_num_moons) # Output: 2 In conclusion, Python provides rich built-in operations for working with strings.
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