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# Python : Formatted String Literals
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{:.no_toc}
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<nav markdown="1" class="toc-class">
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* TOC
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{:toc}
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</nav>
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## The goal
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Using formated string literals is an easy way to produce formated strings from data / variables.
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Questions to [David Rotermund](mailto:davrot@uni-bremen.de)
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## Basic Formatted String Literals
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A formatted string literals starts with an f and the variables that you want to print are placed at their intended position embeded into { }. For example:
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```python
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import numpy as np
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a: str = "Hello"
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b: int = 1
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c: float = np.pi
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mystring: str = f"A: {a} B: {b} C: {c}"
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print(mystring)
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```
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```python
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A: Hello B: 1 C: 3.141592653589793
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```
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In the case the string is to long (i.e. longer than the 80 character limit), you can use this construct to break the line into several lines:
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```python
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import numpy as np
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a: str = "Hello"
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b: int = 1
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c: float = np.pi
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mystring: str = (
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f"Variable A: {a} "
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"Blablablablabla "
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f"Variable B: {b} "
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f"Variable C: {c} "
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)
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print(mystring)
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```
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```python
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Variable A: Hello Blablablablabla Variable B: 1 Variable C: 3.141592653589793
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```
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## [Formats](https://docs.python.org/3/library/string.html#formatspec)
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```python
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format_spec ::= [[fill]align][sign][#][0][width][grouping_option][.precision][type]
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fill ::= <any character>
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align ::= "<" | ">" | "=" | "^"
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sign ::= "+" | "-" | " "
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width ::= digit+
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grouping_option ::= "_" | ","
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precision ::= digit+
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type ::= "b" | "c" | "d" | "e" | "E" | "f" | "F" | "g" | "G" | "n" | "o" | "s" | "x" | "X" | "%"
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```
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### Integer formats
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|||
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|---|---|
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|'b'| Binary format.|
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|'c'| Character.|
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|'d'| Decimal Integer.|
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|'o'| Octal format.|
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|'x'| Hex format. |
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|'X'| Hex format. |
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|'n'| Number.|
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|**None**| **'d'**|
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|||
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|---|---|
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|'+'| indicates that a sign should be used for both positive as well as negative numbers.|
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|'-'| indicates that a sign should be used only for negative numbers (this is the default behavior).|
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|space| indicates that a leading space should be used on positive numbers, and a minus sign on negative numbers.|
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|||
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|---|---|
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|'<'| Forces the field to be left-aligned within the available space (this is the default for most objects).|
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|'>'| Forces the field to be right-aligned within the available space (this is the default for numbers).|
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|'='| Forces the padding to be placed after the sign (if any) but before the digits.|
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|'^'| Forces the field to be centered within the available space.|
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### Float formats
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|||
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|---|---|
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|'e'| Scientific notation.|
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|'E'| Scientific notation.|
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|**'f'**| **Fixed-point notation.**|
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|'F'| Fixed-point notation.|
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|'g'| General format.|
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|'G'| General format.|
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|'n'| Number.|
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|'%'| Percentage. |
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|None| 'g'|
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|||
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|---|---|
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|'+'| indicates that a sign should be used for both positive as well as negative numbers.|
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|'-'| indicates that a sign should be used only for negative numbers (this is the default behavior).|
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|space| indicates that a leading space should be used on positive numbers, and a minus sign on negative numbers.|
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```python
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import numpy as np
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value: float = np.pi
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print(f"{value}")
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print(f"{value:.3f}")
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print(f"{value:+.3f}")
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print(f"{-value:+.3f}")
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```
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```python
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3.141592653589793
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3.142
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+3.142
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-3.142
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```
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```python
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import numpy as np
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value: float = np.pi
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print(f"{value:>30.2f}")
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print(f"{value:<30.2f}")
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print(f"{value:=30.2f}")
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print(f"{value:^30.2f}")
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```
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```python
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3.14
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3.14
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3.14
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3.14
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```
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### String formats
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|---|---|
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|'s'| String format.|
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|**None** | **'s'**|
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### Dates
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```python
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# %%
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from datetime import datetime
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d = datetime.now()
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print(f"{d:%Y-%m-%d %H:%M:%S}")
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```
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```python
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2022-04-03 01:18:45
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```
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| Directive | Meaning | Example |
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|---|---|---|
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|%a|Weekday as locale’s abbreviated name.|Sun, Mon, …, Sat (en_US); So, Mo, …, Sa (de_DE) |
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|%A|Weekday as locale’s full name.|Sunday, Monday, …, Saturday (en_US);Sonntag, Montag, …, Samstag (de_DE)|
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|%w|Weekday as a decimal number, where 0 is Sunday and 6 is Saturday.| 0, 1, …, 6 |
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|%d|Day of the month as a zero-padded decimal number.|01, 02, …, 31 |
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|%b|Month as locale’s abbreviated name.|Jan, Feb, …, Dec (en_US); Jan, Feb, …, Dez (de_DE) |
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|%B|Month as locale’s full name.|January, February, …, December (en_US); Januar, Februar, …, Dezember (de_DE) |
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|%m|Month as a zero-padded decimal number.|01, 02, …, 12|
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|%y|Year without century as a zero-padded decimal number.|00, 01, …, 99|
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|%Y|Year with century as a decimal number.|0001, 0002, …, 2013, 2014, …, 9998, 9999|
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|%H|Hour (24-hour clock) as a zero-padded decimal number.|00, 01, …, 23|
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|%I|Hour (12-hour clock) as a zero-padded decimal number.|01, 02, …, 12|
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|%p|Locale’s equivalent of either AM or PM.| AM, PM (en_US); am, pm (de_DE)|
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|%M|Minute as a zero-padded decimal number.|00, 01, …, 59|
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|%S| Second as a zero-padded decimal number. | 00, 01, …, 59 |
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|%f|Microsecond as a decimal number, zero-padded to 6 digits.|000000, 000001, …, 999999|
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|%z|UTC offset in the form ±HHMM[SS[.ffffff]] (empty string if the object is naive).|(empty), +0000, -0400, +1030, +063415, -030712.345216|
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|%Z|Time zone name (empty string if the object is naive).|(empty), UTC, GMT|
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|%j|Day of the year as a zero-padded decimal number.|001, 002, …, 366|
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|%U|Week number of the year (Sunday as the first day of the week) as a zero-padded decimal number. All days in a new year preceding the first Sunday are considered to be in week 0.|00, 01, …, 53|
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|%W|Week number of the year (Monday as the first day of the week) as a zero-padded decimal number. All days in a new year preceding the first Monday are considered to be in week 0.| 00, 01, …, 53|
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|%c|Locale’s appropriate date and time representation. | Tue Aug 16 21:30:00 1988 (en_US); Di 16 Aug 21:30:00 1988 (de_DE) |
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|%x|Locale’s appropriate date representation. | 08/16/88 (None); 08/16/1988 (en_US); 16.08.1988 (de_DE) |
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|%X|Locale’s appropriate time representation. | 21:30:00 (en_US); 21:30:00 (de_DE) |
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|%%|A literal '%' character.|%|
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see [here](https://docs.python.org/3/library/datetime.html#strftime-and-strptime-format-codes) for the date formats
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## Reference
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* [Formatted String Literals](https://docs.python.org/3/tutorial/inputoutput.html#formatted-string-literals)
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* [Format Specification Mini-Language](https://docs.python.org/3/library/string.html#formatspec)
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