Форматирование вывода печати в Python с помощью f-строки
http://zetcode.com/python/fstring/
Python f-string tutorial
Python f-string tutorial shows how to format strings in Python with f-string.
Python f-string
Python f-string is the newest Python syntax to do string formatting. It is available since Python 3.6. Python f-strings provide a faster, more readable, more concise, and less error prone way of formatting strings in Python.
The f-strings have the
f prefix and use {} brackets to evaluate values.
Format specifiers for types, padding, or aligning are specified after the colon character; for instance:
f'{price:.3}', where price is a variable name.Python string formatting
The following example summarizes string formatting options in Python.
formatting_strings.py
#!/usr/bin/env python3
name = 'Peter'
age = 23
print('%s is %d years old' % (name, age))
print('{} is {} years old'.format(name, age))
print(f'{name} is {age} years old')
The example formats a string using two variables.
print('%s is %d years old' % (name, age))
This is the oldest option. It uses the
% operator and classic string format specifies such as %s and %d.print('{} is {} years old'.format(name, age))
Since Python 3.0, the
format() function was introduced to provide advance formatting options.print(f'{name} is {age} years old')
Python f-strings are available since Python 3.6. The string has the
f prefix and uses {} to evaluate variables.$ python formatting_string.py Peter is 23 years old Peter is 23 years old Peter is 23 years old
We have the same output.
Python f-string expressions
We can put expressions between the
{} brackets.
expressions.py
#!/usr/bin/env python3
bags = 3
apples_in_bag = 12
print(f'There are total of {bags * apples_in_bag} apples')
The example evaluates an expression inside f-string.
$ python expressions.py There are total of 36 apples
This is the output.
Python f-string dictionaries
We can work with dictionaries in f-strings.
dicts.py
#!/usr/bin/env python3
user = {'name': 'John Doe', 'occupation': 'gardener'}
print(f"{user['name']} is a {user['occupation']}")
The example evaluates a dictionary in an f-string.
$ python dicts.py John Doe is a gardener
This is the output.
Python multiline f-string
We can work with multiline strings.
multiline.py
#!/usr/bin/env python3
name = 'John Doe'
age = 32
occupation = 'gardener'
msg = (
f'Name: {name}\n'
f'Age: {age}\n'
f'Occupation: {occupation}'
)
print(msg)
The example presents a multiline f-string. The f-strings are placed between square brackets; each of the strings is preceded with the
f character.$ python multiline.py Name: John Doe Age: 32 Occupation: gardener
This is the output.
Python f-string calling function
We can also call functions in f-strings.
call_function.py
#!/usr/bin/env python3
def mymax(x, y):
return x if x > y else y
a = 3
b = 4
print(f'Max of {a} and {b} is {mymax(a, b)}')
The example calls a custom function in the f-string.
$ python call_fun.py Max of 3 and 4 is 4
This is the output.
Python f-string objects
Python f-string accepts objects as well; the objects must have either
__str__() or __repr__() magic functions defined.
objects.py
#!/usr/bin/env python3
class User:
def __init__(self, name, occupation):
self.name = name
self.occupation = occupation
def __repr__(self):
return f"{self.name} is a {self.occupation}"
u = User('John Doe', 'gardener')
print(f'{u}')
The example evaluates an object in the f-string.
$ python objects.py John Doe is a gardener
This is the output.
Python f-string escaping characters
The following example shows how to escape certain characters in f-strings.
escaping.py
#!/usr/bin/env python3
print(f'Python uses {{}} to evaludate variables in f-strings')
print(f'This was a \'great\' film')
To escape a curly bracket, we double the character. A single quote is escaped with a backslash character.
$ python escaping.py
Python uses {} to evaludate variables in f-strings
This was a 'great' film
This is the output.
Python f-string format datetime
The following example formats datetime.
format_datetime.py
#!/usr/bin/env python3
import datetime
now = datetime.datetime.now()
print(f'{now:%Y-%m-%d %H:%M}')
The example displays a formatted current datetime. The datetime format specifiers follow the : character.
$ python format_datetime.py 2019-05-11 22:39
This is the output.
Python f-string format floats
Floating point values have the
f suffix. We can also specify the precision: the number of decimal places. The precision is a value that goes right after the dot character.
format_floats.py
#!/usr/bin/env python3
val = 12.3
print(f'{val:.2f}')
print(f'{val:.5f}')
The example prints a formatted floating point value.
$ python format_floats.py 12.30 12.30000
The output shows the number having two and five decimal places.
Python f-string format width
The width specifier sets the width of the value. The value may be filled with spaces or other characters if the value is shorter than the specified width.
format_width.py
#!/usr/bin/env python3
for x in range(1, 11):
print(f'{x:02} {x*x:3} {x*x*x:4}')
The example prints three columns. Each of the columns has a predefined width. The first column uses 0 to fill shorter values.
$ python format_width.py 01 1 1 02 4 8 03 9 27 04 16 64 05 25 125 06 36 216 07 49 343 08 64 512 09 81 729 10 100 1000
This is the output.
Python f-string justify string
By default, the strings are justified to the left. We can use the
> character to justify the strings to the right. The > character follows the colon character.
justify.py
#!/usr/bin/env python3
s1 = 'a'
s2 = 'ab'
s3 = 'abc'
s4 = 'abcd'
print(f'{s1:>10}')
print(f'{s2:>10}')
print(f'{s3:>10}')
print(f'{s4:>10}')
We have four strings of different length. We set the width of the output to ten characters. The values are justified to the right.
$ python justify.py
a
ab
abc
abcd
This is the output.
Python f-string numeric notations
Numbers can have various numeric notations, such as decadic or hexadecimal.
format_notations.py
#!/usr/bin/env python3
a = 300
# hexadecimal
print(f"{a:x}")
# octal
print(f"{a:o}")
# scientific
print(f"{a:e}")
The example prints a value in three different notations.
$ python format_notations.py 12c 454 3.000000e+02
This is the output.
In this tutorial, we have worked with Python f-strings.
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