See new Big Daddy Toolbox: Output – format()
Here are a few examples of format() using both syntax structures. Copy and paste in your IDE then compare output to code.

print("A few format() examples:")
print("Run the code, then compare output side by side with code.")

print("(1) Substitution")
name = "Fred"
verb = "swim"
noun = "bannana"
print("One day {} went to {} and found a {}".format(name,verb,noun))
print()

print("(2) Fixed precision at 2 with comma sep - note rounding, up only")
aNumber, bNumber = 12345.6789, -12345.6721
formatString = "15,.2f"
anumString = format(aNumber,formatString)
bnumString = format(aNumber,formatString)
print(anumString, bnumString)
print()

print("(3) as a percentatge with 4 decimal places")
formatString = ">15.4%"
anumString = format(aNumber,formatString)
bnumString = format(bNumber,formatString)
print(anumString, bnumString)
print()

#a little function to save time:
def printnums(Anum,Afor,Bnum,Bfor):
    print("Column Border ->|"+Afor.format(Anum)+"|"+Bfor.format(Bnum)+"|")

print('(4) exponential with a col width of 15')
#a decimal number with two fixed decimal places
formatString = "{:15e}"
printnums(aNumber,formatString,bNumber,formatString)
print()

print("(5) format a header and then data from a string of tuples")
print("     plus adding a space in from of Angler header")
print()
ColHeads=('Species','Weight',"Date","Angler")
print('{:^18}{:<8}{:^10}{:<12}'.format('Species','Weight','Date',' '+'Angler'))
champs=(['spotted bass',10.38,'1/1966','Jones'],['largemouth bass',22.25,'12/1966','Smith'],['rock bass',3.0,'1/1966','Jones'])
for i in range (0,3):
    print('{:<18}{:>8.2f}{:>10}{:<12}'.format(champs[i][0],champs[i][1],champs[i][2],"  "+champs[i][3]))
print()

print("(6 ) formatting a date by calling on datetime")
import datetime
year = 2018
month = 1
day = 19
d = datetime.datetime(year, month, day)
print('{:%m/%d/%Y}'.format(d))   #note the %format specs are a part of datetime(), not format()
print()

print("(7) str() versus repr()")
stringtest="10*2+3.9"
print("This is a test calling str()"+'{!s}'.format(stringtest))
print("This is a test calling repr()"+'{!r}'.format(stringtest))
print()
print('(7b) same format but calling eval inside format')
print("This is a test calling str()"+'{!s}'.format(eval(stringtest)))
print("This is a test calling repr()"+'{!r}'.format(eval(stringtest))) #note no quotes in repr() output