#!/usr/bin/env python
# coding: utf-8

# # Formatting numbers, precision, output

# ## TLDR
# 
# ### Define some constants

# In[86]:


pi = 3.14159265358979323846264338 
Na = 6.0221409e+26                 # #/kmol
atm = 101.325                      # kPa
kB  = 1.3806485279E-23             # J/K
Rg  = 8314                         # J/kmol*K


# ### Format 'em
# * Use a formatted string
#     * ```f"some text, value of var inserted here: {var}"```
#     * That is, ```{var}``` inserts the value of variable ```var```
#     * Can have multiple ```{var}``` in a single string.
# * Format the variable like this ```{var:w.pt}``` 
#     * The format is after the ```:```
#     * ```w``` is the width the variable should take (optional)
#     * ```.p``` is the precision (optional)
#     * ```t``` is the type (optional)
#         * ```e``` for scientific 6.02E23
#         * ```f``` for floating point number 3.14
#         * ```d``` for integer 101
#         * ```s``` for string
#         * etc.

# In[109]:


print(    f"Na  = {Na:20.7e} #/kmol" )
print(    f"atm = {atm:20.3f} kPa"   )
print(    f"Rg  = {Rg:20d} J/kmol*K" )


# ## Details

# 
# There are three main formatting methods. 
# * % formatting
# * str.format()
# * f-strings
# 
# ### Here, we'll use the newer f-string method.
# 
# ### Useful links:
# * [f-string introduction](https://realpython.com/python-f-strings/) with a brief summary of the other methods.
# * [Overview](https://realpython.com/python-string-formatting/) of the three methods.
# * The str.format() and f-string methods have a lot of similiarities.
#     * [This link](https://www.geeksforgeeks.org/python-format-function/) gives a good description of the str.format() method which is good for understanding.
# * [This site](https://pyformat.info) directly compares the older % formatting to the str.format() methods, and gives lots of good examples.
# * Once you already know what is going on, [this short site](https://python-reference.readthedocs.io/en/latest/docs/functions/format.html) gives a pretty complete summary of format codes and options.
# 
# 

# ## Introduction, examples
# * Here, we focus on formatting numbers.
# * Keep things simple, the above links give more details.
# 

# ### Crude printing

# In[47]:


print(  "The value of pi is", pi   )


# ### f-strings
# * This stands for formatted string.
# * Write the string with a leading f
#     * ```f"My string"```
# * Insert variables into the string using {varName}.
#     * ```f"My string {varName}"```
#     * The ```{varName}``` is replaced with the value of the variable.

# In[48]:


print(  f"The value of pi is {pi}"   )


# In[49]:


print(  f"kB={kB} and Na={Na}"   )


# In[50]:


p = f"k={kB} and Na={Na}"
print(p)


# ### Generic python expressions can go inside ```{ }```

# In[51]:


print(   f"pi^2 = {pi**2}"   )


# ### Formating numbers
# * Format as ```{var:t}``` where ```t``` is one of 
#     * ```e``` or ```E``` for scientific, like 6.02E23
#     * ```f``` for floating point, like 3.14
#     * ```d``` for integers, like 101 (d is for decimal number, as opposed to, say, binary)
#     * ```g``` for general number (python chooses), 
#     * (also, ```s``` for string).
#     * other types available, see links above.
#     

# In[93]:


print(    f"Rg = {Rg:d}"   )
print(    f"Rg = {Rg:f}"   )
print(    f"Rg = {Rg:e}"   )


# ### Precision
# 
# * Format as ```{var:.5t}```, where the ```.5``` means 5 decimal places.

# In[64]:


print(    f"pi = {pi:.5f}"    )
print(    f"pi = {pi:.5e}"    )


# ### Width
# * Specify a fixed width of a number.
# * ```{var:w.pt}``` where ```w``` is the full width and ```p``` is the precision.

# In[94]:


print(    f"pi  = {pi:20.5f}"    )
print(    f"Na  = {Na:20.5e}"    )
print(    f"kB  = {kB:20.5e}"    )
print(    f"atm = {atm:20.5f}"   )
print(    f"Rg  = {Rg:20d}"      )


# #### The format codes can be stored as variables
# * If you have lots of print statements you only have to change ```w```, ```p```, and ```t``` below, instead of changing every print statement.

# In[95]:


w = 20
p = 5
t = 'e'
print(    f"Na  = {Na:{w}.{p}{t}}"    )


# ### Right, left, center
# * ```<``` for left
# * ```>``` for right
# * ```^``` for center
# * ```{var:<w.pt}```

# In[102]:


print(    f"kB = {kB:<20.4e} J/K"    )
print(    f"kB = {kB:>20.4e} J/K"    )
print(    f"kB = {kB:^20.4e} J/K"    )


# ### [Click here for more options](https://python-reference.readthedocs.io/en/latest/docs/functions/format.html)