Note that this tutorial concerns NumPy arrays. To learn how to print lists without brackets check out this tutorial:
Problem Formulation
Given a NumPy array of elements. If you print the array to the shell using print(np.array([1, 2, 3])), the output is enclosed in square brackets like so: [1 2 3]. But you want the array without brackets like so: 1 2 3.
import numpy as np my_array = np.array([1, 2, 3]) print(my_array) # Output: [1 2 3] # Desired: 1 2 3
How to print the array without enclosing brackets?
Method 1: Unpacking 1D Arrays
The asterisk operator * is used to unpack an iterable into the argument list of a given function. You can unpack all array elements into the print() function to print each of them individually. Per default, all print arguments are separated by an empty space. For example, the expression print(*my_array) will print the elements in my_array, empty-space separated, without the enclosing square brackets!
import numpy as np my_array = np.array([1, 2, 3]) print(*my_array) # Output: 1 2 3
To master the basics of unpacking, feel free to check out this video on the asterisk operator:
Method 2: Unpacking with Separator for 1D Arrays
To print a NumPy array without enclosing square brackets, the most Pythonic way is to unpack all array values into the print() function and use the sep=', ' argument to separate the array elements with a comma and a space. Specifically, the expression print(*my_array, sep=', ') will print the array elements without brackets and with a comma between subsequent elements.
import numpy as np my_array = np.array([1, 2, 3]) print(*my_array, sep=', ') # Output: 1, 2, 3
Note that this solution and the previous solution work on 1D arrays. If you apply it to arrays with more dimensions, you’ll realize that it only removes the outermost square brackets:
import numpy as np
my_array = np.array([[1, 2, 3],
[4, 5, 6]])
print(*my_array, sep=', ')
# Output: [1 2 3], [4 5 6]You can learn about the ins and outs of the built-in print() function in the following video:
Method 3: Print 2D Arrays Without Brackets
To print a 2D NumPy array without any inner or outer enclosing square brackets, the most simple way is to remove all square bracket characters. You can do this with the string.replace() method that returns a new string by replacing the square bracket characters '[' and ']' with the empty string. To avoid bad indentation, we chain three replacing operations, first replacing the empty space followed by the opening bracket like so: print(str(my_array).replace(' [', '').replace('[', '').replace(']', '')).
import numpy as np
my_array = np.array([[1, 2, 3],
[4, 5, 6],
[7, 8, 9]])
print(str(my_array).replace(' [', '').replace('[', '').replace(']', ''))The output is the 2D NumPy array without square brackets:
1 2 3 4 5 6 7 8 9
Feel free to dive deeper into the string replacement method in this video:
Method 4: Regex Sub Method
You can use the regex.sub(pattern, '', string) method to create a new string with all occurrences of a pattern removed from the original string. If you apply it to the string representation of a NumPy array and pass the pattern '( \[|\[|\])' with escaped brackets to avoid their special meaning (character set), you’ll remove all enclosing square brackets from the output.
import numpy as np
import re
my_array = np.array([[1, 2, 3],
[4, 5, 6],
[7, 8, 9]])
print(re.sub('( \[|\[|\])', '', str(my_array)))The output is:
1 2 3 4 5 6 7 8 9
Note that the same can be accomplished using a character set pattern instead of a group pattern with an optional empty space in front of it:
import numpy as np
import re
my_array = np.array([[1, 2, 3],
[4, 5, 6],
[7, 8, 9]])
print(re.sub(' ?[\[\]]', '', str(my_array)))You can check out my full tutorial on regular expressions if you need a complete guide, or you just watch the regex sub video here:
Method 5: Python One-Liner
To print a NumPy array without brackets, you can also generate a list of strings using list comprehension, each being a row without square bracket using slicing str(row)[1:-1] to skip the leading and trailing bracket characters. The resulting list of strings can be unpacked into the print() function using the newline character '\n' as a separator between the strings.
import numpy as np
my_array = np.array([[1, 2, 3],
[4, 5, 6],
[7, 8, 9]])
print(*[str(row)[1:-1] for row in my_array], sep='\n')The output is:
1 2 3 4 5 6 7 8 9
Feel free to dive into slicing next to boost your coding skills:
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